CHEMISTRY 


OF 


COMMON   THINGS 


BY 


RAYMOND   B.    BROWNLEE 

STUYVESANT    HIGH    SCHOOL 

WILLIAM   J.    HANCOCK 

ERASMUS    HALL    HIGH    SCHOOL 


ROBERT   W.   FULLER 

STUYVESANT    HIGH    SCHOOL  ' 

JESSE   E.   WHITSIT 

DE   WITT   CLINTON    HIGH    SCHOOL 


ALL   OF  NEW  YORK   CITY 


ALLYN    AND    BACON 
Boston  Neto  gotk 


COPYRIGHT,   1914,   BY 

RAYMOND   B.   BROWNLEE,    ROBERT.  W.    FULLER, 
WILLIAM    J.    HANCOCK,  AND  JESSE   E.  WHITSIT. 


d 


Norfaooli 

J.  8.  Cushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

As  the  title  indicates,  this  book  deals  with  the  chemistry  of 
everyday  affairs.  It  is  designed  to  meet  the  growing  demand 
that  high  school  courses  should  prepare  the  pupil  for  citizen- 
ship. In  other  words,  the  book  is  planned  for  that  large  num- 
ber of  students  who  are  limited  to  a  single  course  in  chemistry. 
The  facts  and  principles  of  such  a  course  should  be  of  practical 
use  throughout  life. 

In  an  endeavor  to  meet  the  varying  needs  of  such  students, 
a  wide  range  of  topics  has  been  treated.  This  will  enable  the 
teacher  to  select  a  course  best  suited  to  the  requirements  of 
his  community.  To  this  end,  particular  attention  has  been 
given  to  the  chemistry  needed  for  the  first  courses  in  industrial, 
technical,  and  agricultural  schools,  as  well  as  in  those  teaching 
domestic  science. 

It  is  expected  that  most  schools  will  cover  Part  I,  as  this 
deals  with  such  fundamental  ideas  and  principles  as  chemical 
changes ;  acids,  bases,  and  salts ;  weight  relations ;  chemical 
nomenclature ;  solution ;  oxidation  and  combustion.  More- 
over, Part  I  contains  practical  topics  of  universal  interest, 
such  as  the  chemistry  of  heating  and  lighting ;  air  and  venti- 
lation ;  water  and  its  purification ;  properties  of  metals ;  and 
food  values. 

Part  II  supplies  additional  material  for  courses  adapted 
to  special  needs.  The  authors  have  striven  to  group  a  large 
amount  of  interesting  information  around  scientific  principles, 
and  to  make  it  both  usable  and  scientifically  accurate.  From 
this  second  part,  the  teacher  can  select  the  chapters  best 
adapted  to  the  needs  of  his  particular  school. 

No  apology  is  offered  for  the  omission  from  this  Chemistry 
of  Common  Things  of  certain  theoretical  topics,  traditional  to 


321445 


iv  A  CKNO  WLEDGMENTS 

a  first  course  in  chemistry.  Furthermore,  the  aims  of  this 
book  have  rendered  necessary  a  departure  from  the  familiar 
systematic  study  according  to  elements  and  their  compounds. 
The  authors  believe,  however,  that  the  method  of  treatment 
has  a  sound  scientific  basis,  and  puts  the  chemistry  of  com- 
mon life  into  a  form  at  once  attractive  and  useful. 

NEW  YORK, 

November,  1914. 


ACKNOWLEDGMENTS 

THE  authors  have  been  materially  assisted  in  the  prepara- 
tion of  this  book,  and  particularly  in  the  matter  of.  securing 
material  for  illustrations,  by  the  courtesy  of  members  of  the 
teaching  profession,  of  artists,  and  of  manufacturers.  Credit 
for  copyrighted  pictures  will  be  found  in  connection  with  the 
pictures  themselves.  We  are  under  especial  obligation  to  Mr. 
H.  B.  Judy,  of  the  Brooklyn  Institute  of  Arts  and  Sciences, 
and  to  Mr.  George  Wright,  of  Westport,  Conn.,  for  drawings ; 
to  the  American  Museum  of  Natural  History,  New  York,  and 
to  Professor  L.  H.  Merrill,  of  the  University  of  Maine,  for 
photomicrographs ;  to  Professor  G.  E.  Whipple,  of  Harvard 
University,  for  data  and  illustrations  of  water  purification ; 
and  to  Professor  H.  C.  Sherman,  of  Columbia  University,  for 
data  on  food  values. 

Data  and  illustrative  material  have  also  been  furnished 
by  our  associates,  Messrs.  C.  D.  Griswold,  L.  J.  San,  Ernst 
Schwarzkopf,  and  W.  C.  Uhlig,  of  the  Stuyvesant  High 
School,  and  Mr.  B.  M.  Jaquish,  of  the  Erasmus  Hall  High 
School.  Particular  mention  should  be  made  of  information 
and  drawings  relating  to  the  use  of  illuminating  gas  for  light 
and  fuel  supplied  by  the  Consolidated  Gas  Company  of  New 
York,  and  information  on  aluminum  furnished  by  the  Ever- 
wear  Aluminum  Company.  To  all  of  these  gentlemen  we 
extend  our  hearty  thanks. 


A  CKNO  WLEDGMENTS  V 

Grateful  acknowledgment  is  made  to  the  following  manufac- 
turers for  illustrations  furnished  by  them :  Blaugas  Company 
of  America;  Blaw  Steel  Construction  Company,  Pittsburg; 
Brooklyn  Union  Gas  Company ;  Carborundum  Company ;  Cru- 
cible Steel  Company  of  America;  Dairy  Products  Machine 
Construction  Company,  Derby,  Conn.  ;  Eimer  and  Amend, 
New  York ;  Goldschmidt  Thermit  Company  ;  Dr.  Paul  Heroult, 
New  York ;  International  Acheson  Graphite  Company ;  Inter- 
national Oxygen  Company,  New  York ;  Isbell-Porter  Company, 
Newark,  N.  J. ;  National  Transit  Company,  Oil  City,  Pa. ; 
Ox  weld  Acetylene  Company,  Newark,  N.  J. ;  Oxy- Acetylene 
Appliance  Company,  New  York ;  Prest-0-Lite  Company ; 
Eetsof  Mining  Company,  Retsof,  N.  Y. ;  Ringen  Stove  Com- 
pany, St.  Louis  ;  Simplex  Automobile  Company  ;  Standard  Oil 
Company. 


CONTENTS 

PART  ONE 

CHAPTER 

I.     Chemical  Action        .       •.,•',•••..-.  .  .  1 

II.     Direct  Combination    .         .   ,      »  •       ,  .  ,8 

III.  Acids         .         .    -      .         .         .        v  ;  .  ,  14 

IV.  Bases        .         ...         .         .  .  ,  23 

V.     Salts          .         .  .    •  . •  '    ;,       -.       .,;,•  .  .  33 

VI.     Weight  Relations       .         ,...,,...  44 

VII.     Nomenclature  and  Valence         .    •     v,  .  .  55 

VIII.     Writing  of  Chemical  Equations  .         .  .  .  66 

IX.  Solutions  .  I  j.  .  Iv  .  .  .-..  '-.  .  76 

"  X.  Burning  and  Oxidation  ,  '  .  .  ;  .  ^.  91 

XI.  Fuels  ,  .  /  .  ,:  .  .'  .-  -.:•  101 

XII.  Fireplaces  and  Stoves  .  .  .  .  .  114 

XIII.  Gas  and  Gasoline  Stoves     .         ...  .  .122 

XIV.  Oil  and  Gas  Lights     .         .      ;Y"      -  .  •  •  132 
XV.     Air  and  Ventilation     .        :\ :      ' .  •       .  .  .  144 

XVI.     Chemical  Purification         .   K  _..        .  .  /  157 

N>XVII.     Water       .      .  .   ''      .         .         .         .  '  .  .  167 

:VIII.     Typical  Properties  of  Metals        .         .  .  .  192 

XIX.     Carbon  Compounds    .         .         .         .  .  .  205 

Hydrocarbons,    Substitution    Products,  and 

Alcohols. 

XX.     Carbon  Compounds    .      '   .         .         .  .  .  222 

Aldehydes,  Acids,  Esters,  and  Carbohydrates. 

XXI.     Foods  242 


Vlll 


CONTENTS 


CHAPTER 

XXII. 
XXIII. 
XXIV. 
XXV. 
XXVI. 
XXVII. 
XXVIII. 
XXIX. 
XXX. 
XXXI. 
XXXII. 
XXXIII. 
XXXIV. 
XXXV. 
XXXVI. 
XXXVII. 
VIII. 
XXXIX. 
XL. 
XLI. 
XLII. 
XLIII. 
XLIV. 
XLV. 
XLVI. 


PART   TWO 

The  Cooking  and  the  Adulteration  of  Foods 

Bread  Making 

Milk 

Cream,  Ice  Cream,  Butter,  and  Cheese  . 

Cleaning  and  Laundering 

Ink       ....... 

Textile  Materials 

Dyes  and  Dyeing 

Photography 

Paints,  Oils,  and  Pigments     . 
Distillation  of  Petroleum,  Wood,  and  Coal 
Blast  Lamps  and  Blowpipes   . 
Gas  Engines          .         .  •       .         .  '       •. 
Extraction  of  Metals      .         .         . 
Electric  Furnaces 

Electrochemistry 

Corrosion  of  Metals        .         .         .        -." 
Cleaning  of  Metals      •   .         .         .         ". 
Iron  and  Steel       .         .         .         .         . 

Lime,  Cement,  and  Building  Materials    . 
Brick  and  Pottery          .         .         .       -*^ 
Glass    .         .         .         .         .         .      V 

Commercial  Chemicals          ".-••      .      ;.-•."- 
Agriculture  ...... 

Chemical  Calculations   . 


Physical  Constants  of  the  Important  Elements  . 
Index 


PAGE 

260 
267 
278 
293 
302 
314 
322 
336 
344 
353 
368 
385 
396 
403 
417 
430 
452 
461 
468 
490 
506 
516 
533 
562 
588 

600 
603 


CHEMISTRY    OF   COMMON   THINGS 

CHAPTER   I 
CHEMICAL  ACTION 

1.  Chemical  Change. — A  piece  of  wood  burns  in  an 
open  fire  and  there  is  apparently  nothing  left  but  ashes. 
Fruit  that  is  picked  green  often  ripens,  and  then  decays  if 
kept  too  long.  Milk  becomes  sour  on  standing.  Silver 
and  brass  tarnish.  Cider  left  exposed  to  the  air  changes 


FIG.  1.  — A  WOOD  FIRE. 

to  vinegar.  Whichever  way  we  turn,  we  see  things 
changing  their  nature.  The  change  of  one  substance  into 
another  is  called  a  chemical  change.  To  investigate  and 
explain  these  changes  is  the  object  of  Chemistry.  The 
above  changes  are  quite  complex,  so,  before  attempting  to 

1 


2         *  ,,   CHEMICAL  ACTION 

explain   them,  we    will   take  up   some   simpler   types  of 
chemical  change. 

2.  Decomposition     of    Mercuric     Oxide.  —  The    simplest 
type  of  chemical  change  is  that  in  which  one  material  is 
broken  up  into  two  new  materials.     Let  us  take  a  little  of 
the  red  powder  called  mercuric  oxide  and  heat  it  in  a  test 
tube.     As  the  heating  continues,  we  notice  on  the  cooler 
portions  of  the  tube  drops  of  a  silvery  white  liquid,  which 
we  recognize  as  quicksilver  or  mercury.     While  the  heat- 
ing is  still  going  on,  we   plunge  a   glowing   splinter  of 
wood  into  the  tube  above  the  red  powder,  and  the  splin- 
ter  bursts  into  flame.       As    the    spark   only    glowed   in 
ordinary  air,  the  gas  in  the  tube  must  be  different  from 
air.     It  is  oxygen,  a  gas  which  forms  a  fifth  of  ordinary 
air.      No  one  has  ever   been  able  to  get  anything  but 
mercury    out    of  mercury,  or   anything   but  oxygen  out 
of  oxygen.       The  red  powder  consisted,  therefore,  of   a 
silvery  metallic  liquid  and  a  colorless   gas.       We   have 
changed  the  mercuric  oxide  into  other  things  with  differ- 
ent properties,  and  so  the  change  is  a  chemical  change. 
This  kind  of  change,  in  which  a  substance  is  broken  up 
into  simpler  substances,  is  called  decomposition. 

3.  Decomposition  of  Water.  —  Water  is  the  most  famil- 
iar chemical  compound  that  we  have.     We  know  it  in 
three   forms,  gaseous   water    (steam),  liquid   water,  and 
solid  water  (ice).      We  know  that  no  ordinary  heating 
will  break  water  up  into  simpler  substances,  for  it  simply 
changes  into  steam,  which  may  be  again    condensed   to 
liquid  water.     Decomposition  in  the  case  of  water,  as  in 
many  instances,  may  be  brought  about  by  the  use  of  elec- 
tricity.    Since  pure  water  is  not  a  conductor  of  electricity, 
it  is  necessary  to  add  some  substance,  such  as  sulphuric 
acid  or  caustic  soda,  which  will  make  a  conducting  solu- 


DECOMPOSITION   OF    WATER 


tion.  The  original  amount  of  the  substance  added 
remains  at  the  end  of  the  process,  so  it  is  really  the  water 
that  is  decomposed  by  the  current. 

The  water  may  be  placed  in  the  apparatus  shown  in 
Fig.  2.  ^yhen  the  current  is  passed,  a  cloud  of  fine 
bubbles  surrounds  each  electrode,  but  there  is  a  larger 
cloud  around  the  plate  through  which  the  current  leaves 
the  solution*.  This  plate  is 
called  the  cathode,  which  means 
the  "way  out."  Each  gas  may 
be  separately  collected  by  allow- 
ing it  to  bubble  up  into  tubes, 
previously  filled  with  water, 
and  placed  over  the  ends  of 
the  electrodes.  The  gas,  as  it 
enters  each  collecting  tube,  dis- 
places some  of  the  water.  Ob- 
serving the  rate  at  which  the 
gases  collect,  we  find  that  the 
gas  at  the  cathode  is  liberated 
twice  as  fast  as  that  at  the  other 
electrode  —  the  anode.  Both 
gases  are  colorless,  and  so  we 
cannot  distinguish  them  by  their 
appearance.  But  if  we  apply  a 
flame  to  the  gas  in  the  cathode 
tube,  we  find  that  it  ignites 

with  a  slight  explosion  and  burns  with  a  pale,  almost 
invisible  blue  flame.  This  gas  is  called  hydrogen.  On 
bringing  a  lighted  match  or  splinter  to  the  mouth  of  the 
other  tube,  there  is  no  explosion  and  the  gas  does  not 
burn.  When  the  burning  splinter  is  inserted  in  the  tube, 
it  is  seen  to  burn  more  brightly  ;  a  splinter  that  is  merely 
glowing  will  burst  into  flame.  This  gas  we  recognize  as 


FIG.  2.  —  ELECTROLYSIS  OF 
WATER. 


CHEMICAL  ACTION 


oxygen,  the  same  gas  which  was  liberated  in  the  heating 
of  mercuric  oxide.  When  water  is  decomposed  by  elec- 
tricity, hydrogen  is  liberated  at  the  cathode  and  oxygen 
at  the  anode ;  the  volume  of  the  hydrogen  is  twice  that  of 
the  oxygen.1  By  continuing  the  process  long  enough,  all 
the  water  in  the  tube  could  be  decomposed,  showing  that 
water  consists  of  hydrogen  and  oxygen  only. 


By  courtesy  of  The  Scientific  American. 

FIG.  3. — DIRIGIBLE  BALLOON. 

4.  Properties  of  Hydrogen.  —  As  these  gases  are  very 
important  chemical  substances,  we  will  examine  their 
properties  more  fully.  Hydrogen  is  the  lightest  gas 
known,  being  more  than  fourteen  times  as  light  as  air. 
It  burns  in  air  with  a  transparent  blue  flame  which  is 
often  difficult  to  distinguish.  When  mixed  with  half  its 
volume  of  oxygen  and  ignited,  the  mixture  explodes  with 
fearful  violence.  Water  results  from  the  combination  of 
the  two  gases.  Mixtures  of  hydrogen  and  air,  when 
lighted,  explode  with  different  degrees  of  violence.  The 

1  For  a  fuller  discussion  of  the  electrolysis  of  water  see  Chapter  XXXVII. 


HYDROGEN  AND    OXYGEN  5 

flame  of  burning  hydrogen  is  one  of  the  hottest  known. 
This  flame  may  be  produced  safely  by  means  of  the  oxy- 
hydrogen  blowpipe.  The  blowpipe  consists  of  two  con- 
centric tubes,  so  that  the  gases  may  be  kept  separate  until 
they  unite  in  the  flame  at  the  end.  The  calcium  light, 
used  in  stereopticons  (Fig.  4),  is  produced  by  heating  a 
piece  of  lime  in  an  oxy-hydrogen  flame.  Platinum  and 
other  metals  having  high  melting  points  are  fused  by  the 
use  of  this  blowpipe. 


FIG.  4.  — STEREOPTICON  WITH  CALCIUM  LIGHT. 

5.  Properties    of    Oxygen.  —  Oxygen    is    heavier    than 
hydrogen.     It  is  about  one  ninth  heavier  than  air.     Oxy- 
gen is  slightly  soluble  in  water  —  to  a  sufficient  extent  so 
that  fish  obtain  all  they  need  from  dissolved  air.     Like 
hydrogen,  oxygen  has  no  odor.     Its  most  striking  prop- 
erty is  the  ease  with  which  it  unites  with  a  large  number 
of  substances.       All  cases  of   ordinary  burning   are    the 
uniting  of  oxygen  with  the  coal,  wood,  oil,  or  other  sub- 
stance that  is  being  burned.     The  subject  of  combustion 
will  be  treated  fully  in  Chapters  X  to  XIV. 

6.  Compounds    and    Elements. — We    could    take   other 
familiar  substances  and  break  them  up  into  simpler  ones 


6  CHEMICAL  ACTION 

by  various  processes.  In  all  such  cases,  we  find  that  we 
always  get  the  same  component  parts  from  a  given  sub- 
stance, and  always  in  the  same  proportion.  Thus,  mer- 
curic oxide  always  yields  mercury  and  oxygen,  in  the 
proportion  of  25  parts  by  weight  of  mercury  to  2  of 
oxygen.  Water  is  always  found  to  consist  of  hydrogen 
and  oxygen  in  the  proportion  of  1  part  by  weight  of 
hydrogen  to  8  parts  of  oxygen.  Water  and  mercuric 
oxide  are  examples  of  a  class  of  substances  known  as 
chemical  compounds.  A  chemical  compound  is  a  substance 
consisting  of  simpler  substances,  united  in  an  unvarying 
proportion. 

No  one  has  ever  been  able  to  separate  oxygen,  hydrogen, 
or  mercury  into  any  simpler  substances.  Such  substances 
are  known  as  chemical  elements.  An  element  is  a  sub- 
stance that  has  not  yet  been  decomposed  into  simpler 
substances.  There  are  about  80  elements,  from  which  all 
chemical  compounds  are  made. 

SUMMARY 

A  Chemical  Change  is  a  change  in  the  nature  of  a  substance. 

Decomposition  is  the  change  of  a  substance  into  simpler  sub- 
stances. 

Water  may  be  decomposed  by  electricity  into  the  gases  hydro- 
gen and  oxygen. 

Hydrogen  is  the  lightest  gas  known  and  burns  with  a  very  hot 
flame  in  oxygen  or  in  air. 

Oxygen  is  slightly  heavier  than  air.  Ordinary  combustion  is 
the  uniting  of  oxygen  with  fuel. 

A  Chemical  Compound  is  a  substance  consisting  of  elements 
united  in  unvarying  proportion. 

A  Chemical  Element  is  a  substance  which  has  not  yet  been 
decomposed  into  simpler  substances. 


EXERCISES  7 

EXERCISES 

1.  Give  five  examples  of  chemical  change  not  mentioned 
in  the  chapter. 

2.  Describe  a  test  by  which  a  gas   may  be   recognized  as 
oxygen. 

3.  Tin  when   heated  in  air   changes  into  a  white  powder. 
What  kind  of  a  change  has  taken  place  ? 

4.  To  determine  the  direction  of  current  in  a  circuit  to  be 
used  for  charging  a  storage  battery,  the  wires  are  dipped  into 
acidulated  water.     How  can  the  anode  and  cathode  wires  be 
distinguished  by  observing  the  result  ? 

5.  Why  is  hydrogen  useful  for  filling  balloons  ? 

6.  Why  is  it  dangerous   to  light   the  gas  issuing  from   a 
hydrogen  generator  before  all  the  air  is  out  of  the  apparatus  ? 

7.  Describe  the  oxy-hydrogen  blowpipe  and  give  two  pur- 
poses for  which  it  is  used. 

8.  Fish  will  not  live  in  water  that  has   been  boiled   and 
cooled.     Why  ? 

9.  Distinguish  clearly  between  an  element  and  a  compound. 


CHAPTER   II 

DIRECT  COMBINATION 

Direct  Combination  takes  place  in  the  familiar  phenome- 
non of  burning.  It  was  not  until  a  study  had  been  made 
of  simple  cases  of  direct  combination,  similar  to  those 
described  below,  that  a  knowledge  was  obtained  of  the 
part  played  by  the  oxygen  of  the  air  in  ordinary  burning. 

7.  Mercury    and    Iodine.  —  When   a    little    mercury    is 
placed  in   a  porcelain   mortar  with  a  small  quantity  of 
iodine,  the  two  substances  do  not  lose  their  identity  but 
remain  side  by  side  unchanged.     If,  now,  the  mixture 
is   rubbed  vigorously   with  the  pestle,  a  red   substance, 
which  resembles  neither  mercury  nor  iodine,  is  formed. 
This  new  substance  is  mercuric  iodide: 

mercury  +  iodine  ->mercuric  iodide 
200  "         127  327 

The  number  beneath  the  name  of  each  substance  repre- 
sents the  number  of  parts  by  weight  of  that  substance 
taking  part  in  the  reaction. 

8.  Copper   and  Sulphur.  —  Copper   is   a   reddish-brown 
element.     When  clean  it  reflects  light  in  a  manner  similar 
to  gold,  silver,  nickel,  aluminum,  and  other  elements  called 
metals.     This  brilliancy  is  one  of  the  characteristics  of  a 
metal  and  is  called  metallic  luster.     When  in  thin  strips, 
copper  may  be  easily  bent.     Sulphur  is  a  yellow,  brittle 
element  which  melts  at  a  temperature  only  a  few  degrees 

8 


SIMPLE   TYPES   OF  BURNING  9 

above  that  of  boiling  water.  When  a  small  quantity  of 
sulphur  is  placed  in  a  test  tube  and  held  over  the  flame  of 
a  Bunsen  burner,  it  first  melts  and  later  commences  to 
boil.  If  a  strip  of  thin  sheet  copper  is  thrust  into  the 
vapor  of  boiling  sulphur,  it  becomes  red-hot.  On  remov- 
ing the  strip,  it  is  found  to  have  a  blue-black  color,  to 
possess  a  dull  luster,  and  to  be  very  brittle.  The  strip  no 
longer  possesses  the  characteristic  properties  of  copper; 
neither  does  it  resemble  sulphur.  The  copper  and  sul- 
phur have  united  chemically  to  form  a  new  kind  of 
matter,  copper  sulphide: 

copper  -f  sulphur— >•  copper  sulphide 
63.6  32  95.6 

9.  Tin  and  Oxygen.  —  Tin,  heated  in  oxygen  or  in  air, 
unites  with  the  oxygen  to  form  a  new  substance,  tin  oxide, 
which,  when  pure,  has  a  nearly  white  color. 

tin  -f  oxygen— > tin  oxide 
119      2  x  16  151 

10.  Simple  Types  of  Burning.  —  Many  substances  when 
heated  in  air  take  fire  and  burn  with  a  flame.     A  piece  of 
magnesium  ribbon  when  held  in  a  flame  becomes  hot,  and, 
when  a  definite  temperature  is  reached,  suddenly  bursts 
into  a  flame  of  dazzling  brilliancy.     In  place  of  the  mag- 
nesium, a  white  solid  appears.     This  new  substance  may 
be  easily  crushed  between  the  fingers.     As  the  new  com- 
pound has  exactly  the  properties  of  the  compound  formed 
when  magnesium  is  burned  in  oxygen,  and  is  formed  only 
when  oxygen  is  present,  it  is  known  to  consist  of  magne- 
sium in  chemical  combination  with  oxygen : 

magnesium  +  oxygen— ^magnesium  oxide 
24  16  40 


10 


DIRECT  COMBINATION 


FIG.   5.  —  PHOSPHORUS    COMBINING  WITH 
OXYGEN. 


Phosphorus  takes  fire  at  a  much  lower  temperature  than 
magnesium.  Yellow  phosphorus  will  ignite  if  left  exposed 

to  the  air.  For  this 
reason  it  is  kept  under 
water,  from  which  it 
should  never  be  re- 
moved by  the  bare 
hands.  Red  phosphorus 
takes  fire  less  readily 
than  yellow  phosphorus 
and  is  stored  dry  in  bot- 
tles. When  phosphorus 
burns,  the  chemical  ac- 
tion is  due  to  the  com- 
"bination  of  phosphorus 
with  oxygen  to  form  a  white  solid,  phosphorus  pentoxide : 
phosphorus  +  oxygen ->  phosphor  us  pentoxide 

31  5^  16  111 

~Q 

When  carbon  burns  in  air,  it  unites  with  the  oxygen 

present  to  form  carbon  dioxide  : 

carbon  -4-  oxy  gen ->  carbon  dioxide 
12          2  x  16  44 

11.  Ordinary  Burning.  —  Substances  used  for  fuel  con- 
sist either  of  nearly  pure  carbon,  or  of  compounds  contain- 
ing carbon  and  hydrogen,  or  compounds  containing  carbon, 
hydrogen,  and  oxygen.  Hard  coal,  coke,  and  charcoal  are 
nearly  pure  carbon  ;  burning  oils  are  mixtures  of  com- 
pounds of  carbon  and  hydrogen  ;  illuminating  and  fuel 
gases  consist  of  various  mixtures  of  hydrogen,  compounds 
of  hydrogen  and  carbon,  and  carbon  monoxide  ;  wood  con- 
sists largely  of  carbon  in  combination  with  hydrogen  and 
oxygen.  The  chemical  changes  that  take  place  when  these 
substances  are  burned  are  in  every  instance  similar  to  the 


SUMMARY  11 

simple  types  of  burning  described  above.  The  oxygen  of 
the  air  unites  with  the  carbon  and  hydrogen  of  the  fuel  to 
form  carbon  dioxide  and  steam.  It  is  a  fortunate  provision 
of  nature  that  carbon  dioxide  is  a  gas,  because  about  two 
and  a  half  tons  of  carbon  dioxide  are  formed  when  a  ton  of 
hard  coal  is  burned.  If  this  remained  in  the  stove  or 
furnace  instead  of  passing  out  of  the  chimney,  the  use  of 
coal  as  a  fuel  would  be  practically  impos'sible.  •  Since 
nearly  four  fifths  of  air  consists  of  gases  which  do  not 
support  combustion,  substances  burn  much  more  readily  in 
pure  oxygen  than  they  do  in  air. 

12.  Synthesis.  —  The  building  of  chemical  compounds 
is  called  synthesis.  The  compounds  mercuric  iodide,  copper 
sulphide,  and  the  oxides  just  mentioned,  were  synthesized 
from  their  elements.  In  many  cases,  the  desired  compound 
is  built  from  simpler  compounds. 

SUMMARY 

Mercury  and  Iodine  unite,  when  vigorously  rubbed  together,  to 
form  the  chemical  compound  mercuric  iodide.  This  compound 
contains  200  parts  by  weight  of  mercury  in  combination  with  \2ff 
parts  by  weight  of  iodine. 

Copper  Sulphide  is  formed  when  a  thin  strip  of  copper  is  thrust 
into  the  vapor  of  boiling  sulphur. 

Tin  Oxide  is  formed  when  tin  is  heated  to  a  high  temperature 
in  oxygen  or  in  air.  Magnesium  Oxide  is  formed  when  magnesium 
burns  in  either  oxygen  or  air.  Oxides  of  Phosphorus  and  Carbon 
are  also  readily  formed  by  direct  combination.  In  all  of  these 
cases  the  elements  unite  in  fixed  proportions  by  weight. 

Two  Forms  of  Phosphorus  are  common ;  namely,  red  phosphorus 
and  yellow  phosphorus.  These  have  different  properties  due  to  a 
difference  in  their  energy  content  and  not  to  the  kind  of  matter 
they  contain. 


12  DIRECT  COMBINATION 

In  Ordinary  Burning,  the  elements  contained  in  the  fuel,  chiefly 
carbon  and  hydrogen,  unite  with  the  oxygen  of  the  air  to  produce 
the  compounds  carbon  dioxide  and  steam.  As  these  compounds 
are  colorless,  they  generally  pass  into  the  air  unnoticed.  The 
presence  of  smoke  means  that  a  portion  of  the  fuel  is  not  being 
burned.  About  2i  tons  of  carbon  dioxide  are  formed  for  each 
ton  of  coal  burned.  Nearly  4  of  air  consists  of  gases  which  do 
not  enter  into  combination  with  the  fuel'when  it  burns. 

Synthesis  is  the  building  of  compounds  from  elements,  or  from 
simpler  compounds.  A  synthetic  compound  is  one  that  has  been 
prepared  by  man  from  less  complex  substances. 

EXERCISES 

1.  Give  several  illustrations  of  direct  combination. 

2.  What   evidence  is   there  that  a  new  kind  of  matter  is 
formed  when  mercury  and  iodine  are  rubbed  together  ? 

3.  How  does  the  compound  formed  when  copper  burns  in 
sulphur  differ  from  a  mixture  of  the  two  elements  ? 

4.  Calculate  the   number    of  parts  by  weight  of  mercury 
tjiat  would  unite  with  1  part  by  weight  of  iodine. 

5.  How  many  parts  by  weight  of  iodine  combine  with  25 
parts  by  weight" of  mercury  ? 

6.  How  many  pounds  of  sulphur  would  combine  with  63.6 
pounds  of  copper  to  form  the  compound  copper  sulphide  ? 

7.  How  many  pounds  of  sulphur  would  unite  with  1  pound 
of  copper  ?     With  5  pounds  ? 

8.  Why  was  not  the  phenomenon   of  burning  understood 
until  the  balance  was  used  in  connection  with  chemical  experi- 
ments ? 

9.  How  would  you  show  that  ordinary  burning  is  caused 
by  the  fuel  entering  into  chemical  combination  with  the  oxygen 
of  the  air  ? 


EXERCISES  13 

10.  Can  burning  ever  take  place  without  the  presence  of 
oxygen  ?     Why  do  you  think  so  ? 

11.  Why  is  it  that  matter  appears  to  be  destroyed  when 
wood  or  coal  burns  ? 

12.  If  magnesium  were  as  cheap  as  coal,  why  would  it  still 
be  practically  impossible  to  use  it  as  a  fuel  ? 

£S.   Name  an  element  that  exists  in  more  than  one  form 
ana  tell  about  some  of  the  ways  in  which  the  forms  differ. 

14.  Why   does    the    same   element   sometimes    show   very 
different  properties  ? 

15.  Why  should  riot  yellow  phosphorus  be  handled  with 
the  bare  hand  ? 

16.  What  is  the  meaning  of  the  word  synthesis  ?     Synthe- 
sis of  a  sentence  ?     Synthesis  of  a  chemical  compound  ? 

17.  Can  oxygen  be  prepared  by  synthesis  ?     Explain. 

18.  What  is  synthetic  camphor  ? 

19.  Why  has  synthetic  indigo  largely  displaced  the  natural 
product  ? 

20.  Why  have  much  time  and  money  been  devoted  to  the 
production  of  synthetic  rubber  ? 


CHAPTER    III 

ACIDS 

THE  nickeled  parts  of  gas  stoves  become  worn  and  rusty 
in  use.  Such  parts  are  sometimes  removed,  cleaned,  and 
dipped  in  a  vat  containing  a  solution  of  copper  sulphate  in 
order  to  coat  the  worn  portions  with  copper.  Then  nickel 
is  plated  on  the  copper  coating.  Gold  and  silver  may  be 
recovered  from  plating  solutions  by  placing  certain  metals 
in  the  solutions.  These  actions  depend  upon  the  replace- 
ment of  one  metal  by  another.  To  understand  the  action 
of  an  acid,  we  must  appreciate  what  happens  when  one 

element  replaces  another. 

i 

13.  Simple  Replacement.  —  A  lead  compound  known  as 
lead  nitrate  may  be  made  by  dissolving  lead  in  nitric  acid. 
When  a  bright  strip  of  zinc  is  suspended  in  the  water  so- 
lution of  such  a  compound,  the  surface  of  the  zinc  im- 
mediately becomes  dull.  Soon  the  strip  looks  thicker 
and  longer,  on  account  of  a  dark  glistening  substance 
which  appears  to  be  growing  on  the  zinc  ('Fig.  6).  If 
the  solution  is  left  undisturbed,  the  dark  deposit  may  prq- 
ject  downward  some  distance  into  the  solution.  It  is 
seen  to  consist  of  dark  glistening  scales  arranged  in  a 
branching,  treelike  form.  The  deposit  may  be  easily 
shaken  or  scraped  from  the  strip,  and  when  removed  from 
the  solution  is  in  a  dark,  pulpy  mass.  It  can,  however,  be 
readily  squeezed  into  smaller  bulk  and  changed  by  a  few 
taps  of  a  hammer  into  a  metallic  strip.  This  strip  is 
very  heavy  for  its  size,  can  be  easily  cut  by  a  knife,  and 
can  be  readily  melted  to  a  silvery  liquid.  All  these  prop- 

14 


SIMPLE  REPLACEMENT 


15 


I 


erties  enable  us  to  identify  the  substance  as  lead.  The 
glistening  scales  which  appear  011  the  suspended  zinc 
are  nothing  more  nor  less  than  lead  in  crystalline  form. 

An  examination  of  the 
zinc  strip  shows  that  it  is 
thinner  than  before.  Its 
former  smooth  surface 
is  rough  and  pitted. 
Weighings  show  that 
the  strip  is  not  so  heavy 
as  when  it  was  first 
placed  in  the  solution  of 
the  lead  compound.  Cer- 
tain chemical  tests  prove 
that  there  is  a  zinc  com- 
pound in  the  solution 
where  only  a  lead  com- 
pound was  present  orig- 
inally. This  shows  that 
some  of  the  metallic  zinc 
went  into  solution  at  the 
same  time  that  lead  was 
being  deposited.  We 
may  say  that  zinc  is 
gradually  replacing  the 
lead  in  the  solution,  or, 
more  exactly,  that  the 
zinc  has  taken  the  place  of  the  lead  in  the  dissolved  com- 
pound, forming  a  similar  zinc  compound.  This  may  be 
expressed: 

lead  compound  +  zinc  — >  zinc  compound  -f-  lead 

That  is,  a  metal  in  a  compound  has  been  replaced  by 
another  metal.  Such  a  replacement  of  one  element  by 


FIG.  6. —  REPLACEMENT  OF  LEAD  BY  ZINC. 


16 


ACIDS 


another  element  is  known  as  a  simple  replacement.  There 
are  many  instances  of  simple  replacement  where  one  metal 
replaces  another.  Some  of  the  replacements  are  of  great 
industrial  value.  Copper  of  the  copper  compounds  in  the 
waste  waters  of  copper  mines  is  saved  by  the  use  of  scrap 
iron.  Silver  is  often  recovered  from  its  solutions  by  the 
aid  of  copper  (Fig.  7). 


MG.  7.  —  SILVER  TREE. 


FIG.  8.  —  REPLACEMENT  OF 
HYDROGEN  IN  ACID. 


14.  Acids.  —  It  must  not  be  thought  that  every  simple 
replacement  means  the  replacement  of  one  metal  by 
another.  When  zinc  is  placed  in  hydrochloric  acid, 
bubbles  appear  on  the  surface  of  the  zinc,  break  loose 
from  it,  and  finally  rise  to  the  surface  of  the  liquid  (Fig. 
8).  This  stream  of  bubbles  is  due  to  the  liberation  of  a 
gas  from  the  acid.  The  gas  burns  with  a  pale  blue  flame, 
forming  water  as  the  only  product  of  combustion.  It  is, 
therefore,  hydrogen.  As  the  hydrogen  is  produced  from 


ACIDS  17 

the  acid,  the  zinc  is  gradually  eaten  away.  In  fact,  the 
zinc  has  gone  into  solution,  taking  the  place  of  the  hydro- 
gen, and  forming  a  compound  called  zinc  chloride  : 

zinc  +  hydrochloric  acid  — >-  zinc  chloride  +  hydrogen 

Similarly,  iron,  magnesium,  and  other  metals  will  replace 
the  hydrogen  in  hydrochloric  acid,  or  the  hjdrogen  in  sul- 
phuric acid  and  many  other  acids.  These  actions  are  all 
simple  replacements  in  which  the  hydrogen  of  an  acid  is 
replaced  by  a  metal. 

Compounds  containing  hydrogen  which  can  be  replaced 
by  a  metal,  form  a  large  and  important  class  of  substances 
known  as  acids.  The  possession  of  hydrogen  replaceable 
by  a  metal  is  characteristic  of  acids.  Acids  also  have  a 
sour  taste.  Vinegar  and  lemons  are  sour  because  of  the 
acids  they  contain.  Litmus,  a  vegetable  dye,  is  turned 
red  by  acids.  It  should  be  remembered,  however,  that 
acids  do  not  possess  their  characteristic  properties  unless  dis- 
solved in  water. 

The  replacement  of  the  hydrogen  of  hydrochloric  acid 
may  be  represented  more  completely  as  follows : 

zinc  -h  hydrochloric  acid  — >•  zinc  chloride  4-  hydrogen 

hydrogen  2    1  zinc         65  j 

chlorine     71  J  chlorine  71  J 

Tme  zinc  combines  with  the  chlorine  of  hydrochloric  acid 
toVorm  zinc  chloride,  which  remains  in  solution. 

When  zinc  is  placed  in  dilute  sulphuric  acid,  the  replace- 
ment of  the  hydrogen  of  the  acid  results  in  the  formation 
of  zinc  sulphate  : 

zinc  +  sulphuric  acid    — >-  zinc  sulphate  -f-  hydrogen 


hydrogen    2 

65  sulphur     32 

oxygen     64 


zinc        65 1 

98  sulphur  32     161  2 

oxygen  64  j 


18  ACIDS 

In  this  case,  the  metal  combines  with  that  part  of  sul- 
phuric acid  which  is  not  hydrogen,  forming  zinc  sulphate 
in  solution.  On  the  evaporation  of  this  solution,  the  zinc 
sulphate  is  obtained  as  a  white  solid. 

Iron  sulphate  is  formed  by  the  replacement  of  the  hy- 
drogen of  sulphuric  acid  by  iron.  Such  compounds  as  zinc 
chloride,  zinc  sulphate,  and  iron  sulphate,  which  are  made 
by  the  replacement  of  the  hydrogen  of  an  acid  by  a  metal, 
are  known  as  salts.  The  two  products  formed  by  the  first 
action  of  a  metal  with  an  acid  are  hydrogen  and  a  salt : 

•    metal  -h  acid  — >-  hydrogen  +  a  salt  of  the  metal 

In  many  cases,  the  hydrogen  is  not  given  off  as  a  gas  be- 
cause a  second  action  occurs. 

Acids  are  among  the  most  active  of  chemical  compounds. 
Many  of  them,  as  has  been  stated,  react  vigorously  with 
metals.  Concentrated  sulphuric  acid  chars  wood  and 
paper ;  nitric  acid  attacks  animal  and  vegetable  sub- 
stances ;  hydrofluoric  acid  dissolves  glass.  Another  very 
important  action  of  acids  is  their  behavior  with  bases. 
This  action  will  be  discussed  later. 

15.  Summary :  Characteristics  of  Acids.  — 

(a)  Acids  contain  hydrogen  replaceable  by  a  metal. 
(£)  Acids  react  with  metals  to  form  salts, 
(c)  Acids  taste  sour. 

(<f)  Acids  in  water  solution  turn  blue  litmus  red. 
(e~)  Acids  react  vigorously  with  bases  and  with  many 
other  substances. 

16.  Common  Acids  and  their  Uses.  —  Acids  are  among 
the  most  useful  of  chemical  compounds.     The  agreeable 
taste  and  the  health  value  of  many  fruits  are  due  to  them. 
Citric  acid  is  found  in  the  juice  of  lemons,  oranges,  and 


HYDROCHLORIC  ACID  19 

grapefruit.  Sour  milk  contains  lactic  acid.  Tartaric  acid 
is  obtained  from  crude  cream  of  tartar,  which  is  deposited 
in  wine  vats  during  the  fermentation  of  grape  juice. 

Boric  or  boracic  acid  finds  wide  use  as  a  mild  disinfec- 
tant, e.g.  as  an  eyewash  and  a  mouthwash.  Since  boric 
acid  is  but  slightly  soluble  in  cold  water,  and  it  is  desir- 
able to  obtain  a  saturated  solution  for  these  purposes,  the 
acid  is  dissolved  in  warm  water  and  the  solution  allowed 
to  cool.  Boric  acid  and  its  salts  are  largely  employed  as 
food  preservatives.  It  is  generally  believed  that  this  use 
is  undesirable,  particularly  in  the  case  of  milk  for  infants. 

Tannic  acid  finds  employment  in  the  tanning  of  hides 
into  leather,  in  the  making  of  inks,  and  in  dyeing.  Oxalic 
acid  is  useful  for  cleaning  copper  and  brass,  for  removing 
stains  from  wood,  and  in  the  preparation  of  blue  print 
paper.  In  bleaching,  in  dyeing,  in  calico  printing,  and  in 
the  manufacture  of  drugs  and  chemicals,  acids  are  of 
great  value.  In  general,  it  may  be  stated  that  acids 
play  a  prominent  part  in  many  kinds  of  manufacturing 
operations. 

Many  people  think  incorrectly  that  all  acids  are  color- 
less liquids,  for  the  reason  that  acids  are  commonly  used 
in  water  solutions.  All  of  the  acids  just  mentioned  are 
solids.  While  many  of  the  solid  acids  are  white,  some  of 
them  possess  a  distinctive  color.  Picric  acid,  used  as  a 
remedy  for  severe  burns,  has  a  rich  yellow  color. 

17.  Hydrochloric  Acid  is  the  colorless  gas,  hydrogen 
chloride,  dissolved  in  water.  Concentrated  hydrochloric 
acid  usually  contains  about  one  third  its  weight  of  dis- 
solved hydrogen  chloride ;  the  other  two  thirds  are  water. 
Dilute  hydrochloric  acid  is  usually  made  by  mixing  one 
volume  of  concentrated  acid  with  four  or  five  times  as 
much  water.  Muriatic  acid  is  an  old  name  for  hydro- 


20  A  CIDS 

chloric  acid,  given  because  the  acid  was  made  from  the 
brine  of  the  sea.  This  term  is  now  commonly  used  to 
designate  the  commercial  acid,  which  contains  83  %  of 
hydrogen  chloride. 

18.  Nitric  Acid  is  the  water  solution  of  a  colorless  liquid, 
hydrogen  nitrate,  which  is  about  one  and  a  half  times  as 
heavy  as  water.     Concentrated  nitric  acid  usually  contains 
a  little  more  than  two  thirds  by  weight  of  the  hydrogen 
nitrate.     An  old  name  for  nitric  acid  is  aquafortis  (strong 
water),  given  because  of  its  energetic  action  on  many  sub- 
stances.    Dilute  nitric  acid  is  made  by  mixing  the  con- 
centrated acid  with  four  or  five  times  as  much  water. 

19.  Sulphuric   Acid    was    originally   made    from    green 
vitriol,  a  sulphate  of  iron,  and  was  called  oil  of  vitriol.     It 
is  an  oily  liquid  nearly  twice  as  heavy  as  water.      The 
concentrated  acid  usually  contains  about  7  %  of  water,  the 
remaining  portion  being  the  compound  hydrogen  sulphate. 
Dilute  sulphuric  acid  is  generally  made  by  taking  one 
volume  of  the  concentrated  acid  to  six  volumes  of  water. 
The  mixing  of  the  liquids  should  be  done  with  the  greatest 
care  to  avoid  accidents,  as  the  union  of  the  two  liquids 
produces  great    heat.      The    concentrated  acid  is   slowly 
poured  into  water,  which  is  stirred  constantly. 

20.  Acetic  Acid,  whose  presence  in  a  very  small  amount 
gives  a  sour  taste  to  vinegar,  may  be  bought  in  concen- 
trated form  known  as  glacial  acetic  acid,  so  named  because 
it  solidifies  to  an  icelike  solid  when  the  temperature  be- 
comes several  degrees  below  the  ordinary  room  tempera- 
ture.    This  acid  contains  less  than  5  %  of  water.     Com- 
mercial acetic  acid  contains  about  one  third  its  weight  of 
glacial  acetic  acid. 


EXERCISES  21 

SUMMARY 

Simple  Replacement  is  the  replacement  of  one  element  in  a 
compound  by  another  element.  The  most  familiar  illustrations 
of  this  are  the  replacement  of  one  metal  by  another  and  the  re- 
placement of  the  hydrogen  of  an  acid  by  a  metal. 

Acids  are  compounds  containing  hydrogen  which  can  be  re- 
placed by  a  metal.  Less  important  characteristics  of  acids  are 
the  sour  taste  and  the  turning  of  litmus  red.  An  acid  must  be 
dissolved  in  water  to  show  these  characteristic  properties.  Acids 
react  vigorously  with  bases  and  with  many  other  substances. 
They  are  among  the  most  useful  of  chemicals. 

Salts  are  compounds  formed  by  the  replacement  of  the  hydro- 
gen of  an  acid  by  a  metal,  that  combines  with  the  part  of  the 
acid  that  is  not  hydrogen.  The  salt  formed  remains  in  the 
solution. 

A  Concentrated  Acid  is  the  most  concentrated  water  solution 
of  the  hydrogen  compound  prepared  on  a  large  scale  for  com- 
mercial distribution.  The  amount  of  water  varies  with  the  par- 
ticular acid  ;  for  example,  concentrated  hydrochloric  acid  contains 
about  60%  of  water ;  concentrated  nitric  acid,  about  30%  ;  and 
concentrated  sulphuric  acid,  about  7%. 

A  Dilute  Acid  is  usually  made  by  mixing  any  volume  of  con- 
centrated acid  with  4  to  6  times  as  much  water.  Great  care 
must  be  taken  in  the  preparation  of  dilute  sulphuric  acid. 

Acetic  Acid  is  present  in  small  amounts  in  vinegar.  Glacial 
acetic  acid  contains  less  than  5%  of  water. 

EXERCISES 

1.  What  compound  is  formed  by  dissolving  lead  in  nitric 
acid  ?     How  can  you  get  the  lead  out  of  this  compound  ? 

2.  State  what  happens  when  one  metal  replaces  another  in 
solution. 


22  ACIDS 

3.  Write  a  word  equation  which  shows  how  copper  is  re- 
covered from  the  waste  waters  of  copper  mines. 

4.  Show  how  you  could  obtain  hydrogen  from  sulphuric 
acid  by  simple  replacement.     How  would  you  identify  the 
hydrogen  ? 

5.  Where  does  the  magnesium  go  when  it  is  dissolved  by 
hydrochloric  acid  ? 

6.  Define  an  acid.     What  liquid  must  be  present   for  a 
compound  to  act  as  an  acid  ? 

7.  Write  a  word  equation  and  show  the  weight  relations 
for  the  reaction  of  (a)  magnesium  with  sulphuric  acid ;  (b)  iron 
with  hydrochloric  acid.     (Magnesium  =  24. ;  iron  =  56.) 

8.  Define  a  salt     Name  five  salts. 

9.  Write  the  typical  equation  for  the  reaction  of  a  metal 

with  an  acid. 
• 

10.  What  kind  of  a  compound  is  always  obtained  when  an 
acid  reacts  with  a  metal  ?     Is  hydrogen  always  given  off  ? 

11.  Why  are  acids  considered  active  compounds? 

12.  What  simple   tests   would   enable   you   to   identify   a 
liquid  as  concentrated  sulphuric  acid  ? 

13.  What  is  glacial  acetic  acid  ?      Oil  of  vitrol  ?    Muriatic 
acid  ?     Aqua  fortis  f 

14.  Name  three  foods  that  contain  an  acid.     In  each  case 
name  the  acid. 

15.  Give  directions  for  preparing  700  c.c.  of  dilute  sulphuric 
acid. 

16.  What  are  the  differences  between  hydrogen  chloride, 
concentrated  hydrochloric  acid,  and  dilute  hydrochloric  acid. 

17.  Are  all  acids  liquids  ?     Illustrate. 

16.  Name  an  acid  much  used  by  plumbers.  Which  one  is 
very  useful  in  caring  for  babies  ?  Which  acid  is  necessary  to 
the  body  ? 

19.    Why  are  "  green  apples  "  sour  ? 


CHAPTER   IV 

id 
BASES 

21.  Bases.  —  Bases,  like  acids,  are  very  frequently  en- 
countered in  everyday  life.     The  things  we  know  under 
the  names  of  slaked  lime,  concentrated  lye,  and  ammonia 
water  belong  to  this  class  of  substance. 

The  term  bases  is  applied  to  a  class  of  compounds 
which,  in  some  ways,  may  be  regarded  as  the  opposite  of 
acids  in  chemical  properties.  An  indication  of  this  fact 
is  seen  in  their  action  on  litmus.  Water  solutions  of 
bases  turn  this  dye  from  red  tg  blue,  and  this  fact  is  used 
as  a  test  to  distinguish  soluble  bases  from  acids. 

22.  Preparation    of    Bases.  —  Bases    always    contain    a 
metal.     They  may  be  prepared  in  several  ways  ;  two  of 
the  most  important  are  : 

(a)  by  the  action  of  metals  with  water; 

(5)  by  the  action  of  oxides  of  metals  with  water. 

Thus,  sodium  hydroxide,  one  of  the  most  important  bases, 
is  formed  by  the  action  of  sodium  with  water.  Sodium  is 
a  soft  metal,  easily  cut  with  a  knife,  and  having,  when 
freshly  cut,  a  metallic  luster.  It  combines  with  oxygen 
and  the  moisture  of  the  air  so  readily  that  it  is  kept  under 
kerosene  or  some  oil  that  contains  no  oxygen. 

When  sodium  is  placed  on  water,  there  is  prompt  evi- 
dence of  a  vigorous  chemical  action.  The  metal  melts, 
assumes  a  globular  form,  and  moves  about  the  surface  of 

23 


24  BASES 

the  water  rapidly.  There  is  a  hissing  sound  due  to  the 
liberation  of  a  gas.  This  gas  is  hydrogen.  Potassium 
has  a  similar  but  more  violent  action  (Fig.  9). 

The  water  remaining  in  the  dish  is  found  to  have  new 
properties ;  it  turns  red  litmus  blue,  and  has  a  soapy  feel- 
ing. These  properties  are  due  to  dissolved  sodium  hydrox- 
ide, which  has  been  formed  in  the  action.  On  evaporating 


FIG.  9.  —  POTASSIUM  ON  WATER. 

the  solution,  the  sodium  hydroxide  is  seen  as  a  white 
solid.  This  substance  is  composed  of  three  elements, 
sodium,  oxygen,  and  hydrogen,  the  last  two  in  the  pro- 
portion of  16  parts  by  weight  of  oxygen  to  1  of  hydrogen. 
Bases  alwa}^s  contain  oxygen  and  hydrogen,  and  in  this 
proportion. 

The  action  of   sodium  with  water  can  be  represented 
thus : 


FORMATION   OF   CALCIUM  HYDROXIDE  25 

sodium     +       water  — >-     sodium  hydroxide  4-  hydrogen 


hydrogen  1 

23         oxygen   16 
hydrogen  1 


sodium      23 

18  oxygen      16  [  40  1 

hydrogen    1 


We  see  that  this  is  a  replacement  action.  One  part  by 
weight  of  the  hydrogen  in  water  has  been  replaced  by 
23  parts  of  sodium. 

Calcium,  a  metal  somewhat  resembling  sodium,  reacts 
in  a  similar  way  with  water.  The  action  is  less  violent, 
and  the  base,  calcium  hydroxide,  is  formed.  Since 
it  is  almost  insoluble  in  water,  the  calcium  hydroxide 
can  be  seen  as  it  forms: 

calcium    +  water    — >-     calcium  hydroxide  +  hydrogen 


hydrogen    2 

40  oxygen      32 

hydrogen    2 


calcium     40 

36  oxygen     32  \  74  2 

hydrogen    2 


It  will  be  seen  in  both  these  bases  that  the  hydrogen  and 
oxygen  are  in  the  ratio  of  1  to  16. 

Most  of  the  common  metals,  such  as  iron,  copper,  and 
zinc,  do  not  react  with  water  at  ordinary  temperatures. 
Hence  the  bases  which  they  form  cannot  be  obtained  by 
the  direct  action  of  the  metal  with  water. 

23.  Formation  of  Calcium  Hydroxide.  —  The  two  bases 
of  greatest  practical  importance  are  the  two  whose  forma- 
tion has  just  been  described.  Calcium  hydroxide  is  a 
constituent  of  mortar  and  plaster.  Its  formation  for  this 
purpose  illustrates  another  general  method  for  the  prepa- 
ration of  bases.  The  operation  can  be  seen  going  on 
wherever  a  new  building  is  in  course  of.^  erection.  To 
illustrate  it  in  the  laboratory,  cover  a  few  pieces  of  cal- 
cium oxide,  quicklime,  with  water.  After  a  time,  the  mix- 
ture becomes  hot,  indicating  that  a  vigorous  chemical 
action  is  going  on.  Clouds  of  steam  arise,  and  the  lime 


26  BASES 

soon  crumbles  to  a  powder,  or  becomes  a  pasty  mass  if 
sufficient  water  is  present: 

calcium  oxide       -f-       water     — >•     calcium  hydroxide 

An  i  hydrogen    I }  calcium    40  } 

™S}«       °*ygen  l6  l8       °*ygen  32k 

hydrogen    1 J  hydrogen    2  J 

This  action  is  a  direct  combination.  Notice  again  that 
the  hydrogen  and  oxygen  are  present  in  the  ratio  of  1  to 
16. 

24.  Importance  of  Bases.  —  Unlike    acids,  the  majority 
of   bases   are   insoluble   in    water.     In   discussing   them, 
however,  we  shall  confine  ourselves  chiefly  to  the  soluble 
ones,  including  the   slightly  soluble   calcium  hydroxide. 
The   insoluble   bases  are  of   comparatively   little  impor- 
tance, but  the  soluble  ones  are  among  the  compounds  most 
important  for  the  purposes  of  practical  life. 

Bases  are  very  active  substances  chemically,  especially 
with  (a)  animal  and  vegetable  matter,  (6)  acids. 

25.  Action  on  Animal  and  Vegetable  Matter. — Our  com- 
mon use  of    such  bases  as  concentrated  lye  and  ammo- 
nia water  as  household  cleaning  agents  is  an  illustration 
of  their  power  to  act  with  animal  and  vegetable  matter 
such  as  oils  and  fats,  substances  which  do  not  dissolve  in 
water.     Bases  act  on  them  in  such  a  way  as  to  convert 
them  into  soluble  substances.     Hence  greasy  articles  can 
be  cleaned  with  solutions  of  bases. 

So  great  is  the  chemical  activity  of  some  bases,  how- 
ever, that  they  cannot  be  used  as  cleaning  agents  on  all 
sorts  of  material.  In  cleaning  grease  spots  from  clothing, 
for  example,  ammonia  water  should  be  used  because  its 
action  is  less  energetic  and  because  it  readily  evaporates. 
If  sodium  hydroxide  were  used,  it  would  injure  the  ma- 


ACTION  OF  BASES    WITH  ACIDS  27 

terial,  especially  if  made  of  wool,  which  is  quickly  dis- 
solved by  concentrated  solutions  of  bases.  This  strong 
base  attacks  the  skin  readily  and  should  riot  be  handled 
with  the  bare  hands. 

26.  Soaps.  —  These  substances  are  made  from  fats  by 
boiling  with  bases.     They  may  be  regarded  as  the  bases 
in  modified  form.     They  retain   especially  the   property 
of  dissolving  oils  and  fats,'  and  it  is  for  this  reason  that 
we  use  them  as  cleaning  agents  where  strong  bases  can- 
not  be    used.     Cheap,    coarse    soaps    contain    a    certain 
amount  of   unchanged   base.     It   is  for  this'  reason  that 
they  roughen  the  hands,  or  injure  fabrics  on  which  they 
are  used. 

27.  Alkalies.  —  We  also   use   for   cleaning   purposes  a 
class  of  substances,  which,  while  they  are  not  themselves 
bases,  do  the  work  of  bases,  because  when  dissolved  in 
water  they  form  a  small  amount  of  base  in  the  solution. 
Washing  soda  (sodium  carbonate)  and  borax  are  the  most 
common  substances  used  in  this  way.     The  fact  that  they 
do  form  bases  when  dissolved  in  water  is  shown  by  their 
action  on  litmus,  which  they  turn  from  red  to  blue. 

The  term  alkali  is  applied  to  any  substance  whose  water 
solution  turns  red  litmus  paper  blue.  It  includes  soluble 
bases. 

28.  Action  of  Bases  with  Acids.  —  This  is  a  very  impor- 
tant type  of  action.     As  an  illustration,  consider  the  fol- 
lowing experiment : 

To  a  solution  of  sodium  hydroxide  add  slowly  a  solu- 
tion of  hydrochloric  acid.  The  mixture  becomes  warm, 
showing  that  a  chemical  action  is  going  on.  To  deter- 
mine when  just  the  right  amount  of  acid  has  been  added, 
use  litmus  paper.  Drops  of  the  mixture  are  placed  from 


28 


BASES 


time  to  time  on  litmus  paper  of  each  color.  When  the  solu- 
tion is  neutral,  neither  color  of  paper  will  be  affected.  This 
act  of  mixing  an  acid  with  a  base  in  the  exact  proportion 
for  complete  reaction  with  each  other  is  termed  neutrali- 
zation. On  evaporating  the  neutral  solution,  we  find  that 
a  new  substance,  having  a  definite  crystalline  form  and 
a  characteristic  taste,  has  been  produced.  This  substance 
is  sodium  chloride,  common  table  salt.  Water  was  also 
formed  in  the  reaction  : 


sodium        -4- 
hydroxide 

sodium    231 
oxygen    16     40 
hydrogen  1  j 


hydrochloric 
acid 


water 


sodium 
chloride 


hydrogen    1  ] 
chlorine  35.5  } 


36.5 


hydrogen  1 
oxygen  16 
hydrogen  1 


18 


sodium    23 
chlorine  35.5 


58.5 


Other  examples  of  neutralization  : 

Sodium    hydroxide  and   sulphuric    acid   form    water  and 
sodium  sulphate  : 

sodium  +      sulphuric  — *-  water     4-        sodium 

hydroxide  acid  sulphate 


sodium  46 
oxygen  32 
hydrogen  2 


80 


hydrogen  2 
sulphur  32 
oxygen  64 


hydrogen  2 
oxygen  32 
hydrogen  2 


sodium  46 
sulphur  32 
oxygen  64 


142 


Calcium  hydroxide  and  hydrochloric  acid  form  water  and 
calcium  chloride : 


calcium          +   hydrochloric  —  >•  water  +  calcium 
hydroxide             acid                                        chloride 

calcium  40  "j 
oxygen    32  \  74 
hydrogen  2  J 

hydrogen    21 
chlorine    71  J 

hydrogen  2 
oxygen    32 
hydrogen  2 

calcium    40 
chlorine    71 

111 


It  will  be  noticed  that  water  is  formed  in  all  these  neu- 
tralizations. Such  substances  as  sodium  chloride,  sodium 
sulphate,  and  calcium  chloride  are  known  as  salts. 


COMMON  BASES  AND    THEIR    USES  29 

In  general,  acids  react  with  bases  to  form  (a)  water, 
(5)  a  salt.  This  generalization  is  one  of  the  most  impor- 
tant in  chemistry. 

9 

29.  Summary  :  Characteristics  of  Bases. 

(a)  Bases  always  contain  a  metallic  element  or  group 
of  elements. 

(£>)  Bases  always  contain  hydrogen  and  oxygen  in  the 
ratio  of  1  to  16  by  weight. 

(c')   Bases  in  solution  turn  red  litmus  blue. 

(c?)  Bases  react  with  acids  forming  water  and  salts. 

(e)   Strong  bases  dissolve  many  oils  and  fats. 

30.  Common  Bases  and  their  Uses.  —  Sodium  hydroxide, 
also  called  caustic  soda,  is  obtained  cheaply  from  common 
salt  by  the  use  of  the  electric  current.     It  is  the  most 
important  of  all  bases  from  a  practical  standpoint,  because 
of  its  chemical  activity  and  its  cheapness.    Its  principal  uses 
are  for  making  soaps,  bleaching  compounds,  and  paper  pulp. 

Potassium  hydroxide,  caustic  potash,  is  similar  to  sodium 
hydroxide  and  can  be  used  for  many  of  the  same  purposes. 
It  is  more  expensive,  however,  and  in  soap  making  is  not 
so  desirable,  as  it  commonly  produces  a  soft  soap.  The 
old-fashioned  homemade  soft  soap  was  made  from  the 
potash  (potassium  carbonate)  secured  from  wood  ashes. 

Lye,  or  concentrated  lye,  is  a  term  applied  to  several 
forms  of  strong  bases  sold  commercially.  The  substance 
is  either  sodium  or  potassium  hydroxide,  or  potassium 
carbonate  (potash),  or  a  mixture  of  these.  In  water  solu- 
tion potassium  carbonate  produces  potassium  hydroxide. 

Slaked  lime,  described  above  (§  23)  as  a  constituent  of 
mortar  and  plaster,  has  many  other  practical  uses.  It 
acts  vigorously  on  animal  and  vegetable  matter,  like  the 
stronger  bases,  and  for  this  reason  it  is  used  on  a  large 


30  BASES 

scale  to  remove  hair  from  hides  previous  to  tanning.  It 
is  the  cheapest  base  obtainable,  but  it  is  not  adapted  to 
the  purpose  of  soap  making,  because  the  products  of  its 
action  with  oils  and  fats  are  insoluble  in  water.  For  the 
same  reason  it  cannot  be  used  as  a  direct  cleaning 
agent. 

The  water  solution  of  ammonium  hydroxide,  sold  also 
as  ammonia  water  and  as  spirits  of  hartshorn,  is  especially 
adapted  to  certain  uses  because  the  base  itself  readily 
evaporates,  or  is  "volatile."  The  substance  is  sometimes 
spoken  of  as  the  volatile  alkali.  It  is  much  used  as  a 
cleaning  agent,  especially  for  fabrics,  because  it  readily 
evaporates  and  does  not  remain  in  contact  with  the  cloth 
long  enough  to  do  harm.  It  is  also  an  important 
reagent  in  the  chemical  laboratory. 

Ammonium  hydroxide  is  an  apparent  exception  to  the 
statement  that  a  base  always  contains  a  metallic  element. 
It  is  formed  from  its  elements  in  the  following  proportion  : 
nitrogen  14  parts  by  weight,  hydrogen  4  parts,  which  are 
combined  with  the  usual  1  part  of  hydrogen  and  16  parts 
of  oxygen.  The  combination  of  14  parts  of  nitrogen 
with  4  parts  of  hydrogen  acts  in  many  ways  like  an  ele- 
ment. It  is  spoken  of  as  a  metallic  group.  Just  as  we 
have  ammonium  hydroxide,  we  also  have  many  other 
ammonium  compounds,  such  as  ammonium  chloride  (sal 
ammoniac),  ammonium  sulphate,  and  ammonium  nitrate. 


SUMMARY 

constitute  an  important  class  of  compounds  that  are 
regarded  as  the  chemical  opposites  of  acids.  They  contain  a 
metal  united  to  1  part  of  hydrogen  and  16  parts  of  oxygen. 

Bases  in  solution  turn  litmus  from  red  to  blue.      They  react 
with  acids  to  form  a  salt  and  water. 


EXERCISES  31 

Alkali  is  a  term  which  includes  the  soluble  bases  and  many 
other  substances  that  form  more  or  less  base  when  they  are  dis- 
solved in  water. 

Bases  and  Alkalies  are  useful  as  a  means  of  dissolving  animal 
and  vegetable  matter,  especially  greases.  The  stronger  ones 
form  very  powerful  cleaning  agents  because  of  this  property. 

Soaps  act  like  modified  bases*.  They  are  made -by  boiling  oils 
or  fats  with  strong  bases. 

Important  Soluble  Bases  are  sodium  hydroxide,  potassium 
hydroxide,  and  ammonium  hydroxide.  Calcium  hydroxide  is  a 
strong  base,  but  is  only  slightly  soluble  in  water. 

Other  important  alkalies  are  sodium  carbonate  (washing  soda) 
and  borax. 

EXERCISES 

1.  How  would  you  distinguish  the  solution  of  an  acid  from 
the  solution  of  a  base  ? 

2.  Why  should  care  be  taken  not  to  get  a  solution  of  strong 
base  on  the  hands  ?  On  the  clothing  ?     What  substances  could 
be  used  to  counteract  the  harmful  effects  ?     What  precautions 
should  be  taken  in  applying  these  remedies  ? 

3.  What  base  can  be  applied  to  clothing  without  damage? 
Why  ?     Of  what  practical  use  is  this  fact? 

4.  A  base  is  added  to  the  solution  of  an  acid  until  the  mix- 
ture no  longer  affects  either  color  of  litmus.     What  products 
have  been  formed?     What  general  term  may  be  applied  to  the 
process  ? 

5.  If   acid   were  spilled  on  the  clothing,  what  base  would 
you  apply  ?     Why  ? 

6.  Why   are   soaps  preferred   to   strong  bases   in  cleaning 
clothing  ? 

7.  What  is  a  base  ?    An  alkali  ?     Name  an  alkali  which  is 
not  a  base. 


32  BASES 

8.  What  means  could   be  used   to   quickly  clean   a  very 
greasy  floor?     A  very  greasy  cotton  cloth?     A  very  greasy 
woolen  cloth  ? 

9.  Cheap  soaps  sometimes  contain  free  alkali.      What  are 
the  advantages  and  the  disadvantages  of  such  a  soap  ? 

10.  Why   is   calcium   hydroxide   used   instead    of    sodium 
hydroxide  in  removing  hair  from  hides  in  the  manufacture  of 
leather  ? 

11.  How  can  sodium  hydroxide  be  made  in  the  laboratory  ? 
Write  a  word  equation  for  the  reaction. 

12.  What  very  common  use  is  made  of  calcium  hydroxide 
in  building  operations  ?     How  is  it  prepared  for  this  purpose  ? 

13.  What  are  soaps  ?     How  are  they  made  ? 

14.  What  substance  would  be  used  in  cases  where  a  strong, 
cheap  base  was  required  ? 

15.  Why  is  ammonium  hydroxide  an  apparent  exception  to 
the  fact  that  a  base  always  contains  a  metal  ?     Explain. 


CHAPTER   V 

SALTS 
» 
31.    Sodium   Chloride.  —  Sodium    chloride,    our   familiar 

table  salt,  is  the  most  typical  example  of  a  salt,  as  it 
gives  its  name  to  the  whole  group  of  compounds.  It  is  so 
widely  distributed  that  sensitive  tests  will  show  traces  of 


FIG.  10.  —  INTERIOR  OF  SALT  MINE. 

it  almost  anywhere.  Every  stream  carries  to  the  ocean 
traces  of  salt  dissolved  in  its  waters.  The  reason  for  the 
noticeable  amount  of  salt  in  the  ocean  and  salt  lakes  is 
that  the  water  evaporates,  leaving  the  sodium  chloride. 
Great  beds  of  rock  salt,  formed  by  the  evaporation  of 
some  prehistoric  sea,  are  found  deep  in  the  earth  in  many 


34 


SALTS 


places.  These  salt  deposits  are  sometimes  mined,  as  in 
Poland,  western  New  York,  Michigan,  and  Louisiana 
(Figs.  10,  11).  Another  method  of  working  the  rock  salt 
deposits  is  to  drill  holes  to  the  salt  beds,  force  water  down 
some  of  the  holes,  thus  forcing  the  brine  formed  out 
through  others.  The  brine  is  then  evaporated.  Under- 
ground brine  deposits  are  found  at  a  few  places,  as  at 
Syracuse,  New  York.  Sea  water  furnishes  an  inexhaust- 


FIG.  11.  —  DRILLING  SALT  PREPARATORY  TO  BLASTING. 

ible  source  of  salt,  which  is  separated  in  some  countries  by 
allowing  the  sun's  heat  to  evaporate  the  water  from  shal- 
low reservoirs  (Fig.  12).  In  cold  climates,  the  salt  is 
obtained  by  freezing  sea  water,  the  ice  being  fresh  and 
the  salt  remaining  in  a  concentrated  brine. 

When  brine  is  evaporated  slowly,  as  by  the  heat  of  the 
sun,  the  resulting  crystals  of  salt  are  much  larger  than 
when  more  rapid  evaporation  takes  place.  Table  salt  is 


SODIUM  CHLORIDE 


35 


evaporated  at  the  most  modern  plants  under  very  much 
reduced  pressure,  which  greatly  lowers  the  boiling  point 


Copyright  by  Underwood  &  Underwood. 

FIG.  12.  —  RUSSIAN  SALT  FIELDS.     COLLECTING  SALT  AFTER  EVAPORATION. 

and  increases  the  economy  of  the  process.     Dairy  salt  is 
produced  by  slow  evaporation.     Rock  salt  (Fig.  13)  as  it 


36  SALTS 

comes  from  the  mines  is  used  for  feeding  cattle,  but  most 
of  the  rock  salt  mined  is  crushed,  and  then  sold  for  use  in 
freezing  ice  cream,  preserving  meat,  and  for  the  manufac- 
ture of  other  sodium  compounds.  The  last-mentioned 

use  is  of  enormous  com- 
mercial importance,  as 
such  compounds  as 
washing  soda,  baking 
soda,  and  caustic  soda 
are  manufactured  from 
salt.  Sodium  chloride 
does  not  affect  the  color 
of  litmus,  being  neutral 

in  reaction.     The  cak- 

FIG.  13. —  MASS  OF  ROCK  SALT. 

ing  of  fine  salt  in  damp 

weather  is  chiefly  due  to  magnesium  compounds,  which 
absorb  water  from  the  air. 

32.  Production  of  Salt  by  Neutralization. —  Pure  sodium 
chloride  may  be  made  by  neutralizing  sodium  hydroxide 
with  hydrochloric  acid  : 

sodium      .  hydrochloric  -,.          ui     •  i 

.  _    +    J  — >•  water    +  sodium  chloride 

hydroxide  acid 

sodium      231          hydrogen    11  hydrogen    21         sodium    23     1 

hydrogen    1    40  36.5  j  18    chlorine  35.5     °8'5 

oxygen      16  J 

This  method  is  not  used  commercially,  since  it  is  much 
more  expensive  than  the  purification  of  natural  salt. 
Many  other  salts,  however,  are  made  by  the  neutralization 
of  the  base  containing  the  metallic  portion  of  the  salt 
with  the  acid  containing  the  non-metallic  portion.  For  it 
must  be  remembered  that  one  product  of  neutralization 
is  always  a  salt  (§  28). 


ACTION  OF  AN  ACID    WITH  A   METAL  37 

33.  Production  of  Salts  by  the  Action  of  Acid  and  Metal.  — 

When  zinc  is  treated  with  hydrochloric  acid,  hydrogen  is 
liberated  and  the  zinc  replaces  the  hydrogen  in  the  acid, 
forming  zinc  chloride  (§  14) : 

zinc  +  hydrochloric  acid  — >•  zinc  chloride  +  hydrogen 

When  more  acid  is  used  than  is  necessary  to  dissolve  the 
zinc,  the  acid  solution  formed  is  very  efficient  in  cleaning 
the  surface  of  metals.  It  is  frequently  used  as  a  solder- 
ing fluid,  to  remove  the  oxides  from  the  pieces  to  be 
soldered  together,  so  that  the  solder  will  adhere  more 
firmly  to  the  metal. 

It  will  be  remembered  that  zinc  sulphate  is  produced  in 
a  similar  way  by  the  action  of  zinc  with  sulphuric  acid 
(§14): 

zinc  +  sulphuric  acid  — *-  zinc  sulphate  -f-  hydrogen 
The  zinc  sulphate  is  obtained  in  transparent  crystals  by 
evaporation  of  the  solution  formed.  It  is  often  called 
white  vitriol.  It  is  used  in  calico  printing  and  in  electric 
batteries.  In  like  manner,  sodium  chloride  might  be 
formed  by  the  action  of  sodium  with  hydrochloric  acid, 
but  the  action  would  be  so  violent  as  to  be  extremely 
dangerous.  Magnesium,  dropped  into  dilute  hydrochloric 
acid,  decomposes  the  acid,  liberating  hydrogen  and  taking 
its  place  to  form  magnesium  chloride: 

sodium  -h  hydrochloric  acid  — >-  SO(        fl  +  hydrogen 

chloride 

magnesium  -{-hydrochloric  acid — ^ma£nesmm  +  hydrogen 

chloride 

A  salt  is  a  product  formed  by  the  replacement  of  the 
hydrogen  of  an  acid  by  a  metal. 

34.  Action  of    a  Metallic    Oxide  with   an  Acid —  Cold 
dilute  sulphuric  acid  does  not  act  on  copper,  so  copper 


38  SALTS 

sulphate  cannot  be  made  by  simple  replacement.  Copper 
oxide,  however,  readily  reacts  with  dilute  sulphuric 
acid  : 

copper  oxide  +  sulphuric  acid  — >•  copper  sulphate  -j-  water 

.  hydrogen    2 1  copper    63.6 

££«>•«  -**«  ?  «  ""*«« 

oxygen      64  J  oxygen  64 


159.6     hydrogen    21 
oxygen      16  j 


This  fact  is  utilized  in  one  process  of  manufacture  of 
copper  sulphate. 

It  will  be  seen  that  the  oxide  method  of  forming  a  salt 
is  closely  similar  to  the  method  of  neutralization.  In  both 
cases  the  products  formed  are  water  and  a  salt.  This 
illustrates  the  fact  that  oxides  of  the  metals  behave  to  a 
certain  extent  like  bases. 

In  cases  in  which  the  oxide  reacts  more  readily  than 
the  metal,  the  method  of  obtaining  salts  from  the  oxide  is 
much  employed  commercially.  In  some  cases,  compounds 
other  than  the  oxide  are  employed,  on  account  either  of 
their  low  price  or  of  their  special  adaptation  to  the  forma- 
tion of  the  salt  desired.  These  will  be  noted  in  connec- 
tion with  the  different  compounds. 

35.  Important  Salts.  —  Potassium  chloride  closely  re- 
sembles sodium  chloride  in  appearance  and  general  prop- 
erties. It  is  the  only  soluble  potassium  compound  occur- 
ring in  extensive  deposits.  The  chief  use  of  potassium 
chloride  is  as  a  raw  material  for  the  manufacture  of  other 
potassium  compounds.  The  most  important  deposit  of 
the  salt  is  at  Stassfurt  in  Germany,  where  potassium 
chloride  and  some  other  salts  form  a  great  underground 
bed,  resembling  the  rock  salt  deposits  mentioned  earlier. 
As  potassium  chloride  is  not  so  widely  distributed  as 
sodium  chloride,  the  latter  is  used  in  chemical  manufac- 


IMPORTANT  SALTS  39 

tures  in  which  a  chloride  is  necessary  and  the  metal  is  not 
important. 

Potassium  nitrate  (saltpeter)  is  a  familiar  salt  used  in 
the  preservation  of  meat  and  in  the  manufacture  of  gun- 
powder. It  is  sometimes  called  niter.  It  is  usually  pro- 
duced commercially  by  treating  sodium  nitrate  with  po- 
tassium chloride : 

sodium        potassium         potassium     ,        n.          ,,     ., 

-h  1  ^  +  sodium  chloride 

nitrate  chloride  nitrate 


sodium  23 
nitrogen  14 
oxygen  48 


85 


potassium  39 


potassium  39 


*?;r~r       IT  K     74.5    nitrogen     14 
chlorine     35.5  J 

oxygen       48 


1A1   sodium   23     \ 
101  chlorine  35.5  I58'5 


The  above  process  could  not  be  carried  on  if  saltpeter  were 
not  much  more  soluble  in  hot  water  than  is  salt.  It  is  an 
interesting  example  of  how  some  special  property  enables 
us  to  manufacture  a  valuable  chemical  from  more  abundant 
and  less  expensive  materials.  The  sodium  nitrate  comes 
from  Chile,  where  there  are  extensive  beds,  and  it  is  called 
Chile  saltpeter.  It  is  extensively  used  as  a  fertilizer  and 
in  the  manufacture  of  nitric  acid. 

Sodium  sulphate  is  manufactured  by  the   reaction   be- 
tween salt  and  sulphuric  acid : 

sodium         sulphuric  sodium    ,11      11-        -j 

. .,     +  — >.  +  hydrochloric  acid 

chloride  acid  sulphate 


._  ,  hydrogen    2 

sodium    46  1  .,,_       J,  , 

117     sulphur     32 

oxygen      64 


chlorine  71 


sodium  46 

98     sulphur  32 

oxygen  64 


hydrogen    2  1  ?3 


chlorine    71 


There  are  two  interesting  things  about  this  reaction. 
One  is  that  we  get  two  valuable  substances  from  a  single 
action  —  sodium  sulphate  and  hydrochloric  acid.  The 
other  is  the  double  replacement  that  takes  place  :  sodium 
replaces  hydrogen  in  sulphuric  acid,  forming  sodium  sul- 
phate, and  hydrogen  replaces  sodium  in  sodium  chloride, 


40 


SALTS 


forming  hydrochloric  acid.  Sodium  sulphate  is  familiar  as 
a  medicine  under  the  name  of  Glauber's  salt.  Large  quanti- 
ties of  the  crude  compound  are  used  in  glass  manufacture. 
Magnesium  sulphate  (Epsom  salts)  occurs  in  consider- 
able quantities  in  mineral  deposits  and  is  found  in  many 
mineral  waters.  It  is  prepared  for  medicinal  purposes  by 
purifying  the  natural  compound. 

Ammonium  chloride  is  familiarly 
known  as  sal  ammoniac.  When 
soft  coal  is  heated  in  closed  retorts 
for  the  purpose  of  driving  off  the 
volatile  matter  to  form  illuminating 
gas,  the  base  ammonium  hydroxide 
is  obtained  as  a  by-product.  When 
this  is  neutralized  with  hydrochloric 
acid,  ammonium  chloride  is  the  salt 
formed.  This  is  used  in  batteries 
for  ringing  doorbells  (Fig.  14);  for 
cleaning  soldering  irons,  and  for 
many  purposes  in  chemical  manufactures. 


FIG.  14. 


36.  Salts  which  are  not  Neutral.  —  Many  salts  are  not 
neutral  like  sodium  chloride,  but  turn  litmus  red  or  blue, 
thus  indicating  the  presence  of  an  acid  or  a  base  in  the 
solution.  Thus,  copper  sulphate  gives  an  acid  reaction 
and  zinc  sulphate  behaves  in  a  similar  manner.  In  these 
cases  the  salt  reacts  with  the  water  in  which  it  is  dis- 
solved, forming  a  very  small  quantity  of  sulphuric  acid. 
Sodium  carbonate  (soda)  and  borax  (sodium  biborate), 
on  the  contrary,  form  basic  solutions  when  they  are  dis- 
solved in  water.  In  each  of  these  cases,  the  salt  has  re- 
acted with  the  water,  forming  a  small  proportion  of 
sodium  hydroxide.  The  use  of  borax  and  soda  in  clean- 
ing depends  upon  their  alkaline  properties.  It  is  con- 


SUMMARY 


41 


venient  to  remember  that  salts  which  are  formed  by  the 
reaction  of  an  active  acid  with  a  weak  or  comparatively 
inactive  base  usually  have  an  acid  reaction,  e.g.  copper 
sulphate.  The  reaction  of  an  active  base  with  a  weak 
acid  gives  such  basic  salts  as  soda  and  borax. 


SUMMARY 

IMPORTANT  SALTS 


COMMON  NAME 

CHEMICAL  NAME 

SOURCE 

USES 

Salt 

Sodium  chloride 

Ocean,  salt 

Source  of  sodium 

wells,  and 

and  chlorine  com- 

mines 

pounds.     Many 

Potassium 
chloride 

Deposits  in  Ger- 
many 

minor  uses 
Source  of  potassium 
compounds 

Saltpeter 

Potassium 
nitrate 

Made  from 
sodium  nitrate 

Curing  meat;   gun- 
powder 

Chile  saltpeter 

Sodium  nitrate 

Deposits  in 
Chile 

Fertilizer  ;  manu- 
facture of  nitric 

acid 

Glauber's  salt 

Sodium  sulphate 

Salt  and  sul- 
phuric acid 

Medicine  ;  glass 
manufacture 

Epsom  salts 

Magnesium 
sulphate 

Natural  deposits 

Medicine 

Sal  ammoniac 

Ammonium 
chloride 

Manufacture  of 
illuminating 

Battery  fluid 

gas 

Washing  soda 

Sodium 
carbonate 

Made  from  so- 
dium chloride 

Washing  ;   mild  al- 
kali ;  glass  manu- 
facture 

Borax 

Sodium  biborate 
Zinc  chloride 

Borate  deposits 
Zinc  and  hydro- 
chloric acid 

Softening  hard  water 
Soldering  fluid 

White  vitriol 

Zinc  sulphate 

Zinc  and  sul- 
phuric acid 

Calico  printing  ; 
battery  fluid 

Blue  vitriol 

Copper  sulphate 

Copper  and  sul- 
phuric acid 

Fungicide  ;  battery 
fluid 

42  SALTS 

Common  Salt  is  sodium  chloride.     It  is  obtained  from  natural 
deposits  of  rock  salt  or  by  the  evaporation  or  freezing  of  brine. 

Neutralization  is  the  production  of  water  and  a  salt  by  the  re- 
action between  an  acid  and  a  base. 

Salts  may  be  formed  by  the  replacement  of  the  hydrogen  in 
acids  by  metals. 

Metallic  Oxides  react  with  acids,  producing  water  and  salts. 

Salts  Neutral  to  Litmus  are  produced  by  the  reaction  of  a  strong 
base  with  a  strong  acid. 

Salts  Alkaline  in  Reaction  are  produced  by  the  reaction  of  a 
strong  base  and  a  weak  acid. 

Salts  Acid  in  Reaction  are  produced  by  the  reaction  of  a  weak 
base  and  a  strong  acid. 

EXERCISES 

1.  Why  are  the  Great  Lakes  not  so  salt  as  the  Great  Salt 
Lake? 

2.  Describe  two  methods  of  obtaining  salt  from  solution. 

3.  Give  five  industrial  uses  of  sodium  chloride. 

4.  Write  word  equations  for  four  cases  of  neutralization. 

5.  What  will  be  produced  if  solutions  of  potassium  hydrox- 
ide and  hydrochloric  acid  are  mixed?     Solutions  of   sodium 
hydroxide  and  sulphuric  acid  ? 

6.  Name  a  compound  that  is  always  formed  during  neutral- 
ization. 

7.  Why  is  hydrochloric  acid  frequently  used  for  cleaning 
metals  ? 

8.  Give  three  ways  in  which  magnesium  chloride  may  be 
made. 

9.  Name    two    salts    used    in   soldering.      Why    are    they 
used  ? 


EXERCISES  43 

10.  Explain,  with  illustrations,  how  the  cost  of  raw  mate- 
rial, the  conditions  under  which  the  reaction  takes  place,  and 
the  production  of  useful  by-products  determine  the  commercial 
process  for  producing  a  salt. 

11.  Give  the  chemical  names  of  common  salt ;  blue  vitriol ; 
saltpeter ;  Epsom  salts  ;  sal  ammoniac ;  borax. 

12.  Would  you  expect  copper  nitrate  to  be  neutral,  acid,  or 
alkaline  in  reaction  ?     Give  reason. 

13.  Large  quantities  of  sodium  carbonate  are  used  in  the 
refining  of  kerosene,  which  has  previously  been  treated  with 
sulphuric  acid.     On  what  property  of  sodium  carbonate  does 
this  use  depend  ? 

14.  Why  are   washing   soda  and   borax  used   in  washing 
clothes  ? 

15.  Explain,  with  an  example,  what  is  meant  by  double 
replacement. 


CHAPTER   VI 


WEIGHT  RELATIONS 

37.  Importance  of  Weight  Relations.  —  In  the  develop- 
ment of  chemistry  the  study  of  weight  relations  has 
played  a  very  important  part.  It  is  only  by  comprehend- 
ing these  relations  that 
we  can  gain  certain 
important  aids  for  un- 
derstanding chemical 
ideas. 

To  illustrate  what  is 
meant  by  the  determi- 
nation of  weight  rela- 
tions we  will  consider 
the  following  experi- 
ment. A  small  quan- 
tity of  copper  is  weighed 
in  a  crucible.  Sulphur 
is  added  and  the  cruci- 
ble is  heated  until  the 
copper  has  Combined 
with  sulphur  and  the 
excess  of  sulphur,  if  any,  has  been  driven  off  by  heat. 
The  crucible,  which  should  now  contain  nothing  but 
copper  sulphide,  is  allowed  to  cool  and  is  again  weighed. 
The  following  data  are  thus  obtained.  Actual  weights 
are  given  to  serve  as  an  example. 

44 


FIG.   15.  —  ANALYTICAL  BALANCE. 


REACTING    WEIGHTS  45 

(#)  Weight  of  crucible  +  copper       .     .     .     .  7.37  g. 

(5)  Weight  of  crucible 6.32g. 

(<?)  Weight  of  copper 1.05  g. 

(d)  Weight  of  crucible  +  copper  sulphide       .  7.89  g. 

O)  Weight  of  crucible 6.32  g. 

CO  Weight  of  copper  sulphide 1.57  g. 

(g)  Weight  of  sulphur  .     .     .     .     .     .     .     .  0.52  g. 

This  experiment  shows  that  1.05  g.  of  copper  requires 
0.52  g.  of  sulphur  to  form  copper  sulphide.  We  may  also 
say  that  the  relative  quantities  of  the  two  elements  are 
expressed  by  the  ratio  1.05  :  0.52.  Notice  that  this  ratio 
may  be  expressed  with  sufficient  accuracy  in  simpler 
terms,  since  one  of  the  numbers  is  almost  exactly  half 
the  other.  The  ratio  then  becomes  2:1.  If  ,we  wish 
we  may  put  the  ratio  in  still  other  terms,  such  as  4 :  2  or 
20 : 10,  without  altering  its  value.  This  shows  what 
we  mean  when  we  speak  of  relative  numbers.  In  any 
particular  experiment,  the  weights  of  copper  and  sulphur 
may  be  very  large  or  very  small,  but  the  weight  of  the 
copper  will  always  be  twice  the  weight  of  the  sulphur. 

Weight  relations  can  be  found  in  this  way  for  all  the 
elements  that  enter  into  combination  with  each  other. 
Early  in  the  history  of  chemistry  it  was  noticed,  on  com- 
paring two  weight  ratios  in  which  one  of  the  two  elements 
was  the  same,  that  a  remarkable  regularity  existed. 

38.  Reacting  Weights.  —  To  make  this  regularity  easily 
seen  it  is  necessary  to  have  a  system  for  expressing  the 
rati'os.  This  is  done  by  finding  for  each  element  the 
weight  of  it  that  combines  with  16  parts  of  oxygen. 
Oxygen  is  chosen  for  the  standard  because  most  of  the 
elements  combine  with  it ;  the  value  is  placed  at  16  be- 
cause this  is  a  whole  number  and  is  large  enough  to  avoid 
making  the  number  for  hydrogen,  the  lightest  element, 


40  WKI11UT  HNLATIONN 

IONN  Minn   1,      Wo  will  Mpmlt  of  the  immhor  MM  found   for 
oaoh  olomont  UN  UN  rttafltln//  my/hi.     A   fow  of  thorn  urn 
UN  I'ollowN  : 

MutfiioNimn    ,     .....       24 

/inn     ......     ,     ,       65 

Mnronry    .....  •  ,     ,     UOO 

Chlorine   ,    ,    .....      71 

Hulphur    .......       Hi 

Tin  ,     II!) 

Now  nxuminn  tho  wni^ht  rutioN  for  Novoml  rompoundM 
(ofined  by  coiuhinitl  ioiiH  ninoii^1  tlio  ubovo  ulotiUMitH  : 

/inn  Nulphido,  y.iiui  OA  pari.H,  Niilplmr  H2  piirU  ; 

Mngneiiutn  ehloride,  ntagnoNiiun  tJ4  PIU-IM,  ohlorino  71 
purl  M  ;  • 

Morourid  olilorido,  tnoroury  '200  piirtN,  ohlorino  71  purt.M  ; 

Tin  ohloridt,  tin  1  1!'  pin-In,  ohiorino  1  IU 


four  ration  MM   found    ixperiinonlully   would   of 

ooune  give  ui  ratloi  exprtMttd  Inimilltrnumben.  In  oaoh 
uiMt\  tlio  two  toi'tttH  of  llui  ratio  liavo  luuut  multiplied  by 
"•  ii  a  nnntlmr  that  thu  ilrnt  tonn  will  bo  tin-  roactin^ 
woi^ht  an  ^ivon  in  tlto  abovo  lubl--  for  that  olomont. 
NotiM  that  tht>  tMond  number  i*  aho  nthvr  the  rmotiny 
wriyht  f/ivtn  in  tht*  tnltltt  or  a  multiple  qf  it.  Thin  IH  tlio 
"rwnarkablo  roj^nlarity  "  rofoi-rod  to  abovo,  and  in  ono  of 
tho  prinoipal  roaHonn  for  tho  invontion  of  tho  atontio 
hypothoHiN,  an  alnumt  indiHponNablo  aid  for  tho  Mtrniy  of 
ohoiniHtry, 

39.    LAW  of  Definite  Proportion!.      Tho  furls  Htatnl  \\\ 
§§  H7   and   JW  aro  oiubodiod   in   (wo  IUWM  (li'Ht  H(II(IM|   \\\ 
1805  by  John'Dalton,  an  lOn^liHh  oluMniHt.     llo  ulsu  •!< 
viMoil  tho  atoinio  hypotheell  an  an  oxplunation  of  thcso  laws. 
llo  llrNt  Ntutod  tho  vorv  Hintplo  faot  tiiat  ovory  ohonn'oal 


ATOMN  IV 

Compound  alwayn  han  the  name  olomentM  in  the  name  pro- 
portion  hy  weight.     The  iiHiuil  Mhiicmniit  nl'  the  law  IN 

/'//  '*'/'//    <i/li-nin->l/      ,.'iil/'»illl</      Jl,tH     <t      ih'jillitt'      <'<»>!  /KtHl't  l<Hl      lit/ 

//•»•//////.       Any    Miilmtanoo    which    follow*    thin    law    in    a 
xupotiiul  ;  anything  thnt  <|<M<M  not.  in  a  ini 


(Mx 


•IO  Law  nl  Miiltipln  I'lopoi  I  IOM-I  Th(^  MIM'OIK!  law  (IniiU 
with  l.linMo  niMoM  ill  which  two  or  more  CKIII|  KiiuiiU  arn 
formed  from  I.  ho  HUIIIC  cIciiuuilH,  l^or  cxamphs  nitrogen 
nnd  oxygon  foi-ni  llv(^  difl'onmli  (inuipouiKlH  an  fnllnwNi 


COMI'MIINII 

Nil  lluiil'N 

UH 

OH  VllKIN 
HI 

ai 

JI'J 

UH 

4N 

UH 

II! 

N  il.i-M^'i'ii  pnntoxliln     ,      ,     i           i      i      i     i      i      i      , 

98 

MO 

The  nil  ro^rcii  iiiiinliiM'  in  liikcn  U,K  *JH  in  ciich  CIIMC  ;  we  then 
MIT  Mm!  the  oxy^nn  iiiiinhiu'K  tire  nil  rxnrl  niiilliplcM  of  HI, 
Thn  law  may  he  Minted  I  IIIIH  ;  77/r  n>i'i<//it  r<i(i'<>H  t»r  <'<>m 

jHt'HHlln  fomil'tl  f'fntn    t/H1   HifllH'    ••/I'llH'HfH   H/HHt'   (I    )HH/(i/>/<    I'f'i 
(toil   III  I  III'   <lH<IH(i(il'H  nf  OHt'   t'/t'HH'll(i  //    I  III'   of/Iff   IM  Ifl'/tf    fil'l'lf. 

41.  A  torn  I.  !(/  will  he  MOOII  from  whni  II.IM  heen  nl-uied 
that,  wo  may  think  nfu.n  element  a*  poKHewKin^  a  niimhor, 
or  net  of  iiiunhci'H,  which  oxproNMOH  the  purtH  hy  weight  of 
I!M  element  which  enter  intn  (mentic<al  action.  'Mm 
oxygon  (iilwayM  rememherin^  that  we  are  limiting  our 
IN'  .1  MM  infill.'!  mi  it  c<nn/mr<i(ii't'  «ir  I'lMicI  in^  weight  NyHtem) 
entei'N  intn  c.omhinai ion  only  hy  IO'H,  JJii'n,  'IH'n,  or  Home 
other  niimher  hearing  a  multiple  rehilion  to  10.  ('hlorine 
c.omhincM  with  (<»r  rnphu-rM)  other  elementH  only  hy  Hr».f» 


48  WEIGHT  RELATIONS 

parts,  71  parts,  142  parts,  or  some  other  multiple  of  35.5. 
A  similar  thing  is  true  for  each  of  the  other  elements. 

As  a  reasonable  explanation  of  these  facts  and  of  many 
others  which  cannot  be  discussed  here,  chemists  suppose 
that  an  element  is  composed  of  particles,  called  atoms, 
which  have  the  following  characteristics  : 

(a)  They  are  extremely  small. 

(£)  All  the  atoms  of  the  same  element  have  the  same 

weight,  which  is  the  unit  weight  that  enters  into 

chemical  combination. 
(<?)  They  do  not  divide  in  chemical  action  (this  is  the 

reason  that  oxygen,  for  example,  always  reacts 

by  16's,  32's,  etc.). 

42.  Molecules.  —  It  is  a  further  part  of  our  belief  that 
chemical  compounds,  such  as  water,  sodium  hydroxide,  etc., 
are  composed  of  groups  of  atoms  of  different  elements. 
Thus  sodium  chloride  is  believed  to  be  made  up  of  small 
groups,  each  consisting  of  one  atom  of  sodium  united  with 
one  atom  of  chlorine  ;   water  to  be  made  up  of  groups, 
each  consisting  of  two  atoms  of  hydrogen  united  to  one 
atom  of  oxygen.     A  single  one  of  these  groups  is  called  a 
molecule.     They  are  so  extremely  small  that  even  a  mi- 
nute particle  of  a  compound  contains  millions  of  them. 
A  molecule  is  the  smallest  division  of  a   substance   having 
the  properties  of  the  mass. 

43.  Symbols  of  Elements.  —  A  system  of  symbols  is  used 
to  express  in  a  simple  way  the  relative  weights  and  other 
facts  concerning  atoms  and  molecules.     To  represent  an 
atom,  we  use  the  first  letter  of  the  name  of  the  element,  in 
many  cases  taking  the  Latin  name  ;   often  a  second  letter 
is  necessary  because  the  names  of  two  elements  begin  with 


FORMULAS   OF  COMPOUNDS  49 

the  same  letter.     Usually  the  second  letter  taken  is  signifi- 
cant in  the  pronunciation  of  the  name  of  the  element. 

O  means  16  parts  by  weight  of  oxygen. 

H  means  1  part  by  weight  of  hydrogen. 

S  means  32  parts  by  weight  of  sulphur. 

C  means  12  parts  by  weight  of  carbon. 

Cl  means  35.5  parts  by  weight  of  chlorine.* 

Ca  means  40  parts  by  weight  of  calcium. 

Na  (from  Latin  natrium)  means  23  parts  by  weight  of 
sodium. 

K  (from  Latin  kalium)  means  39  parts  t  by  weight  of 
potassium. 

Fe  (from  Latin  ferrum)  means  56  parts  by  weight  of 
iron. 

Ag  (from  Latin  argentum)  means  108  parts  by  weight 
of  silver. 

44.  Formulas  of  Compounds.  —  To  represent  a  molecule 
of  a  compound,  we  write  in  succession  the  symbols  of  the 
elements  composing  the  compound,  in  each  case  following 
the  symbol  by  a  subscript  number  to  represent  the  partic- 
ular multiple  of  the  weight  that  enters  into  the  combina- 
tion. Where  the  multiple  is  one,  the  digit  is  not  written 
but  is  understood.  For  example  : 

H2O  represents  a  molecule  of  water,  weighing  18  parts 
on  our  relative  scale,  and  composed  of  2  parts  of  hydrogen 
(2  atoms)  and  16  parts  of  oxygen  (1  atom). 

HC1  represents  one  molecule  of  hydrogen  chloride, 
weighing  36.5  parts,  composed  of  1  part  of  hydrogen  (1 
atom)  and  35.5  parts  of  chlorine  (1  atom). 

Na2SO4  represents  one  molecule  of  sodium  sulphate, 
weighing  142  parts,  composed  of  46  parts  of  sodium  (2 
atoms),  32  parts  of  sulphur  (1  atom),  and  64  parts  of 
oxygen  (4  atoms). 


50 


WEIGHT  RELATIONS 


45.    Atomic  Weights  of  Important  Elements. 


Aluminum 

.     .      27 

Iodine  .     .     . 

.    127 

Phosphorus 

.     .     31 

Barium 

.     .    137 

Iron       .     .     . 

.      56 

Platinum     . 

.     .  195 

Bromine 

.     .      80 

Lead     .     .     . 

.    207 

Potassium  . 

.     .     39 

Calcium 

.     .     40 

Magnesium    . 

.     24 

Silicon    .     . 

.     .     28 

Carbon  .     . 

.     .      12 

Manganese     . 

.      55 

Silver     .    . 

.     .  108 

Chlorine     . 

.     .  35.5 

Mercury    .     . 

.    200 

Sodium  .     . 

.     .     23 

Copper  .     . 

.     .  63.6 

Nickel  .     .     . 

.      59 

Sulphur  .     . 

.     .     32 

Gold  .     .     . 

197 

Nitrogen   . 

.      14 

Tin     . 

119 

Hydrogen  . 

.     .        1 

Oxygen      .     . 

.      16 

Zinc   .     .     . 

.     .     65 

46.  Atomic  and  Molecular  Weights.  — The  numbers  given 
in  the  table  (§  45)  are  spoken  of  as  atomic  weights.     They 
are  believed  to  express  the  relative  (comparative)  weights 
of  the  atoms  of  the  different  elements.     The  standard  is 
the  weight  of  the   oxygen   atom,   placed  at   16,  for   the 
same  reasons  that  governed  our  choice  of  a  standard  for 
reacting  weights. 

The  weight  of  a  molecule  of  a  compound  is  the  sum  of 
the  weight  of  the  atoms  which  compose  it.  Molecular 
weights  can  be  determined  directly  by  experiment. 

47.  Formulas  of  Some  Substances.  —  (T?or  reference  only.) 


Acetic  acid,  HC2H3O2 

Ammonium  chloride,  NH4C1 

Ammonium  hydroxide,  NH4OH 

Borax,  Na2B4O7 

Calcium  hydroxide,  Ca(OH)2 

Calcium  oxide,  CaO 

Carbon  dioxide,  CO2 

Citric  acid,  H3C6H5O7 

Copper  sulphate,  CuSO4 

Copper  sulphide,  CuS 

Hydrochloric  acid,  HC1 

Hydrogen,  H2 

Lead  nitrate,  Pb(NO3)2 

Magnesium  oxide,  MgO 

Magnesium  sulphate,  MgSO4 


Mercuric  oxide,  HgO 
Nitric  acid,  HNO3 
Oxalic  acid,  H2C2O4 
Oxygen,  O2 

Phosphoric  acid,  H3PO4 
Phosphorus  pentoxide,  P2O5 
Potassium  chlorate,  KClOj 
Potassium  hydroxide,  KOH 
Potassium  nitrate,  KNO3 
Silver  nitrate,  AgNO3 
Sodium  bicarbonate,  NaHCOg 
Sodium  carbonate,  Na2CO8 
Sodium  chloride,  NaCl 
Sodium  hydroxide,  NaOH 
Sodium  sulphate,  Na2SO4 


EQUATIONS  FOR   SOME  REACTIONS  51 

Sulphuric  acid,  H2SO4  Water,  H2O 

Tartaric  acid,  H2C4H4O6  Zinc  nitrate,  Zn(NO3)0 

Tin  oxide,  SnO2  Zinc  sulphate,  ZnSO4 

48.    Equations  for  Some  Reactions.  —  (For  reference  only.) 
Decomposition  of  mercuric  oxide  : 

2HgO—  ^2Hg  +  02      . 

Decomposition  of  water  by  the  electric  current  : 
2H20—  ^2H2  +  02 

Formation  of  copper  sulphide  : 
Cu  +  S— 

Formation  of  tin  oxide  : 

Sn  +  O2— 

Formation  of  mercuric  iodide  : 


The  burning  of  magnesium  : 
2Mg+02— 

The  burning  of  phosphorus  : 
4P  +  502  —  ^ 

The  burning  of  carbon  : 

C  +  02—  ^ 

Replacement  of  lead  by  zinc  : 

Pb(NO3)2  +  Zn  —  -»-  Zn(NO3)2  4-  Pb 

Replacement  of  hydrogen  in  hydrochloric  acid  by  zinc 
Zn  +  2HCl— 


Replacement  of  hydrogen  in  sulphuric  acid  by  zinc  : 
Zn  +  H2SO4  —  ^-  ZnS04  +  H2 


52  WEIGHT  RELATIONS 

Action  of  magnesium  with  hydrochloric  acid  : 
Mg  +  2  HC1  — ->-  MgCl2  +  H2 

Action  of  copper  oxide  with  sulphuric  acid  : 
CuO  +  ff2SO4— >-  CuSO4  +  H2O 

Action  of  sodium  nitrate  with  potassium  chloride  : 
NaNO3  +  KC1  ^±  KNO3  +  NaCl 

Action  of  sodium  chloride  with  sulphuric  acid  : 
2  NaCl  +  H2SO4— ^Na2SO4  +  2  HC1 

SUMMARY 

Study  of  the  Weight  Relations  of  chemical  compounds  reveals 
certain  regularities  known  as  the  Law  of  Definite  Proportions  and 
the  Law  of  Multiple  Proportions. 

Law  of  Definite  Proportions :  Every  chemical  compound  has  a 
definite  composition  by  weight. 

Law  of  Multiple  Proportions :  The  weight  ratios  of  compounds 
formed  from  the  same  elements  show  a  multiple  relation  in  the 
quantities  of  one  element  if  the  other  is  kept  fixed. 

These  Laws  are  Explained  by  Atomic  Theory.  According  to 
this  theory,  the  elements  are  composed  of  particles  which  are : 
(a)  extremely  small,  (£)  of  the  same  weight  for  a  given  element, 
and  (c)  indivisible  in  chemical  action. 

Molecules  are  the  smallest  divisions  of  a  substance  having  the 
properties  of  the  mass.  They  consist  of  one,  two,  or  more 
atoms.  They  do  not  break  up  in  physical  change,  but  do  in 
chemical  change. 

Atomic  Weights  are  numbers  that  express  the  comparative  or 
relative  weights  of  the  atoms  of  different  elements.  The  basis 
of  this  comparative  system  is  the  weight  of  the  atom  of  oxygen,  16. 


EXERCISES  53 

Symbols  are  letters  that  stand  for  atoms,  and  hence  weights  ot 
the  elements.  O  means  1  atom  of  oxygen,  weight  16;  N  means 
1  atom  of  nitrogen,  weight  14. 

Formulas  used  to  represent  molecules,  and  hence  weights  of 
substances,  are  aggregations  of  symbols  followed  by  numerals, 
expressed  or  understood.  They  indicate  the  composition  of  the 
substance.  H2O  stands  for  18  parts  by  weight  of  water,  and 
indicates  that  the  substance  is  composed  of  2  parts  of  hydrogen 
and  16  parts  of  oxygen. 

A  Molecular  Weight  is  the  sum  of  the  weights  of  the  atoms 
that  make  up  a  molecule  of  a  substance. 

EXERCISES 

1.  What  is  meant  by  the  term  relative  quantities?     Illus- 
trate.    What  is  meant  by  the  term  ratio?     Illustrate. 

2.  How  would  you  determine  the  reacting  weight  of  mag- 
nesium ? 

3.  What  uniformity  or  regularity  is  observed  by  inspecting 
the  reacting  weights  of  different  elements? 

4.  What  is  meant  by  saying  that  oxygen  enters  into  com- 
bination only  by  16's?     Chlorine  by  35.5's? 

5.  According   to   the   atomic   theory,   what  characteristics 
have  atoms?    • 

6.  What  is  the  atomic  weight  of  an  element  ?     What  is  the 
atomic  weight  of  oxygen?    Explain  why  this  number  is  chosen 
as  a  standard. 

7.  What  are  molecules? 

8.  Give    symbols    for    the    elements   sulphur,   magnesium, 
iron,   sodium,   chlorine,    potassium.     What    does  the   symbol 
mean  in  each  case  ?     What  are  molecular  weights  ? 

9.  What  is  the  formula  for  water?     What  does  it  mean? 
What  is  the  formula  for  sodium   sulphate?     What    does  it 
mean  ? 


54  WEIGHT  RELATIONS 

10.  A  molecule  of  magnesium  chloride  consists  of  one  atom 
of  magnesium  and  two  atoms  of  chlorine.    Write  a  formula  for 
the  substance.    -What  is  the  weight  composition  of  magnesium 
chloride? 

11.  A  molecule  of  iron  (ferrous)  sulphate  consists  of  one 
atom  of  iron,  one  atom  of  sulphur,  and  four  atoms  of  oxygen. 
What  is  its  formula?     What  is  its  weight  composition? 

12.  State  the  Law  of  Definite  Proportions. 

13.  State  the  Law  of  Multiple  Proportions. 

14.  The  weight  composition  of  hydrogen  peroxide  is  32  parts 
of  oxygen  to  2  parts  of  hydrogen.     Show  how  the  composition 
of  this  compound  and  the  composition  of  water  illustrate  the 
law  of  multiple  proportions. 

15.  Calculate  the  molecular  weight  of  sulphuric  acid,  H2S04. 

16.  Write  the  equations  given  in  §  48,  placing  the  name  of 
each  substance  beneath  its  formula. 

Note  to  Instructor.  —  The  equations  in  §  48  were  given  for  reference 
only.  Until  he  has  studied  Chapters  VII  and  VIII,  the  student  is  not 
expected  to  do  anything  more  with  them  than  is  required  by  this  Exercise 
16. 


CHAPTER  VII 
NOMENCLATURE  AND  VALENCE 

A  NUMBER  of  examples  of  simple  equations  have  been 
given.  The  writing  of  chemical  equations  requires  a 
knowledge  of  the  chemical  changes  involved,  an  acquaint- 
ance with  nomenclature,  and  the  remembrance  of  valence. 
The  rules  for  the  naming  of  inorganic  acids,  bases,  and 
salts  are  simple  and  can  be  learned  with  little  difficulty. 

49.  Binary  Compounds  are  those  that  contain  two  ele- 
ments.    Sometimes  a  group  of  elements  plays  the  r61e  of 
the    positive    element.     Binary    compounds    have    names 
ending  in  -ide.     The  ending  -ide  is  added  to  a  root  de- 
rived  from    the    name   of   the   negative    element   (§  51) 
entering   the    molecule.      Binary   compounds    containing 
oxygen  are  oxides,  those  containing  chlorine  are  chlorides, 
those    containing  sulphur  are  sulphides,  etc.     This  rule 
does  not   apply  to  compounds  of  carbon  and  hydrogen, 
on  account  of  the  large  number  of  such  substances  known. 

50.  Valence  is  the  term  used  to  designate  the  combin- 
ing power  of  one  atom  of  an  element,  or  that  of  a  group 
of  atoms  acting  like  an  element,  compared  with  the  com- 
bining power  of  the  hydrogen  atom.     If  one  atom  of  an 
element  will  combine  with  one  atom  of  hydrogen,  or  if 
one  atom  of  an  element  can  replace  one  atom  of  hydrogen 
in  a  compound,  the  element  is  said  to  have  a  valence  of 
one. 


56  NOMENCLATURE  AND    VALENCE 

51.  Positive  and  Negative   Elements.  —  The  element   is 
negative  if,  on  the  electrolysis  of  the  compound,  it  is  at- 
tracted to  the  positive  electrode  (anode),  and  positive  if 
it  is  attracted  to  the  negative  electrode    (cathode).     In 
general,  elements  that  combine  with  hydrogen  are  nega- 
tive,   while   those    that   replace   hydrogen    are    positive. 
Usually  positive  elements  are  metals  and  negative  ele- 
ments are  non-metals.     Chlorine,  bromine,  and  iodine  are 
common  negative  elements  having  a  valence  of  one.     In 
addition  to  these,  it  is  convenient  to  consider  the  hydroxyl 
group,  OH,  as  being  a  negative  group  having  a  valence  of 
one.     Thus  we  have  the  compounds 

hydrogen  chloride,  HC1, 
hydrogen  bromide,  HBr, 
hydrogen  iodide,  HI, 

and  water,  which  might  be  called 

hydrogen  hydroxide,  HOH. 
The  same  element  may  have  more  than  one  valence. 

52.  Important    Valences.  —  The    common    positive    ele- 
ments having  a  valence  of  one  are  sodium,    potassium, 
copper  in  cuprous  compounds,  silver,  and  mercury  in  mer- 
curous  compounds.     In  connection  with  these,  the  student 
should  remember  the  group  NH4,  called  the  ammonium 
group.     Thus,  corresponding  to   hydrogen   chloride,    we 
have 

ammonium  chloride,  NH4C1,  cuprous  chloride,  CuCl, 

sodium  chloride,  NaCI,  silver  chloride,  AgCl, 

potassium  chloride,  KC1,  mercurous  chloride,  HgCl. 

Sulphur  and  oxygen  combine  with  two  atoms  of  hydro- 
gen. They,  consequently,  have  a  valence  of  two  and  are 
negative  elements : 


IMPORTANT   VALENCES  57 

hydrogen  sulphide,  H2S, 
water,  H2O. 

One  atom  of  each  of  the  elements  magnesium,  calcium, 
zinc,  and  barium  will  take  the  place  of  two  atoms  of  hy- 
drogen. They  are  positive  elements  having  a  valence  of 
two.  Binary  compounds  in  which  iron  and  tin  have  a 
valence  of  two  ar6  termed  respectively  ferrous- compounds 
and  stannous  compounds  ;  those  in  which  copper  and 
mercury  have  a  valence  of  two  are  termed  respectively 
cupric  compounds  and  mercuric  compounds.  It  will  be 
noticed  that  the  ending  -ous  refers  to  the  less  and  the  end- 
ing -ic  to  the  greater  yalence  of  the  positive  element.  The 
chlorine  compounds  of  the  elements  just  mentioned  may 
be  taken  as  illustrations  of  compounds  of  positive  elements 
having  a  valence  of  two  : 

magnesium  chloride,  MgCl2,  zinc  chloride,  ZnCl2, 

calcium  chloride,  CaCl2,  stannous  chloride,  SnCl2, 

•ferrous  chloride,  FeCl2,  barium  chloride,  BaCl2, 

cupric  chloride,  CuCl2,  mercuric  chloride,  HgCl2. 

The  elements  aluminum,  chromium,  and  iron  (in  ferric 
compounds)  are  positive  in  most  of  the  compounds  the 
beginner  is  likely  to  meet,  and  have  a  valence  of  three. 
Thus  we  have  the  compounds 

A1C13,  aluminum  chloride,  CrCl8,  chromium  chloride, 

FeCl8,  ferric  chloride. 

Carbon,  silicon,  and  tin  (in  stannic  compounds)  have 
a  valence  of  four.  The  only  important  exception 
to  this  is  carbon  monoxide,  CO,  in  which  the  valence 
of  carbon  is  two. 

CC14,  carbon  tetrachloride,  SiCl4,  silicon  tetrachloride, 

SnCl4,  stannic  chloride. 


58  NOMENCLATURE  AND    VALENCE 

The  elements  nitrogen,  phosphorus,  arsenic,  antimony, 
and  bismuth  commonly  have  a  valence  of  either  three  or  five. 

53.  Prefixes  indicating  Number  of  Atoms.  —  The  terms 
mono-  (one),  di-  (two),  tri-  (three),  tetra-  (four),  and 
penta-  (five)  are  frequently  used  to  indicate  the  number 
of  atoms  of  the  element  before  whose  name  the  prefix  is 
placed.  For  example, 


CO  is  carbon  monoxide,         Pg^s'  phosphorus  trioxide, 
CO2,  carbon  dioxide,  ^V^s'  phosphorus  pentoxide, 

CC14,  carbon  tetrachloride. 

54.  Satisfaction  of  Valences.  —  In  a  molecule  there  are 
as  many  positive  valences  as  there  are  negative  valences. 
One  atom  of  a  positive  element  having  a  valence  of  one 
can  unite  with  one  atom  of  a  negative  element  having  the 
same  valence,  while  two  atoms  of  a  positive  element  hav- 
ing a  valence  of  one  would  be  required  to  combine  with 
one  atom  of  a  negative  element  having  a  valence  of  two. 
Three  atoms  of  a  positive  element  having  a  valence  of  two 
would  be  required  to  combine  with  two  atoms  of  a  nega- 
tive element  having  a  valence  of  three,  and  so  on. 

The  valences  given  are  the  common  ones  the  beginner 
is  likely  to  meet.  As  he  advances,  he  will  learn  of  cases 
where  the  elements  have  other  valences  than  those  given 
in  this  chapter,  but  by  that  time  he  is  likely  to  be  so  fa- 
miliar with  formulas  that  the  new  valences  will  cause  little 
trouble. 

55.  Electrochemical    Series.  —  The    terms    positive    and 
negative  applied  to  elements  are  relative.     It  is  possible 
to  arrange^  the  elements  so  that  each  is  positive  to  any 
element  placed  above  it   and   negative   to   any   element 
placed  below  it.     The  following  shows  the  more  common 
elements  thus  arranged: 


NOMENCLATURE  OF  ACIDS 


59 


Negative  end. 
Oxygen 
Sulphur 
Nitrogen 
Chlorine 
Bromine 
Iodine 
Phosphorus 
Arsenic 
Chromium 
Boron 
Carbon 
Antimony 
Silicon 
Tin 

Hydrogen 
Gold 

'Platinum 
Mercury 
Silver 
Copper 
Bismuth 
Lead 
Nickel 
Iron 
Zinc 

Manganese 
Aluminum 
Magnesium 
Calcium 
Strontium 
Barium 
Sodium 
Potassium 
Positive  end. 


56.  Bases.  —  A  base  is  the   hydroxide   of 
a  metal,  or  the  hydroxide  of  a  group  of  atoms 
playing  the  role  of  a  metal.     The  common 
bases  are 

ammonium  hydroxide,  NH4OH, 
sodium  hydroxide,  NaOH, 
potassium  hydroxide,  KOH, 
calcium  hydroxide,  Ca(OH)2. 

57.  Nomenclature  of  Acids.  — The  formulas 
for  simple  acids  and  salts,  and  the  names  of 
the  corresponding  compounds,  may  be  readily 
mastered  if  the  student  will   take   time   to 
commit  to  memory  the  names  and  formulas 
of  a  few  acids  which  contain  oxygen  and  have 
names  ending  in  -ic.    These  acids  and  formulas 
are  — 

nitric  acid,  HNO3, 
chloric  acid,  HC1O3, 
sulphuric  acid,  H2SO4, 
phosphoric  acid,  H3PO4, 
carbonic  acid,  H2CO3. 


The  names  are  formed  by  adding  -ic  to 
a  root  derived  from  the  characteristic  nega- 
tive element  contained  in  the  acid.  This 
root  may  be  the  entire  name  of  the  negative 
element,  as  in  the  case  of  the  sulphur  acids ; 
or  it  may  be  a  part  of  the  name  of  the  nega- 
tive element,  as  in  the  case  of  the  acids  of 
chlorine,  where  chlor-  is  the  root.  Having 
committed  to  memory  the  name  and  formula  for  the 
-ic  acid,  the  names  and  formulas  for  other  acids  of  any 
series  may  be  obtained  by  application  of  the  following 
rules : 


60  NOMENCLATURE  AND    VALENCE 

An  acid  containing  one  less  atom  of  oxygen  than  the  -ic  acid 
has  its  name  formed  by  the  addition  of  -ous  to  the  root. 
HC1O2  is  chlorous  acid ;  H2SO3,  sulphurous  acid. 

If  the  acid  contains  less  oxygen  than  the  -ous  acid,  its 
name  is  formed  by  prefixing  hypo-  to  the  name  of  the  -ous 
acid.  HC1O  is  the  formula  for  hypochlorous  acid. 

An  acid  containing  more  oxygen  than  the  -ic  acid  has  its 
name  formed  by  prefixing  per-  to  the  name  of  the  -ic  acid. 
HC1O4  is  the  formula  for  perchloric  acid. 

When  the  acid  contains  no  oxygen,  its  name  is  formed 
by  prefixing  hydro-  to  the  name  of  the  -ic  acid.  HC1  is 
the  formula  for  hydrochloric  acid. 

58.  Nomenclature  of  Salts. — Normal  salts  are  those  in 
which  all  of  the  replaceable  hydrogen  of  an  acid  has  been 
exchanged  for  a  metal.     When  an  acid  contains  oxygen 
and  has  a  name  ending  in  -ic,  salts  of  that  acid  end  in 
-ate.     If  the  acid  ends  in  -ous,  salts  of  that  acid  end  in 

-ite.     Salts  of  hypo ous  acids  end  in  -ite.     The  names 

of  the  sodium  compounds  illustrating  these  rules  are  given 
in  the  Summary  under  the  heading  of  Salts  (page  64). 

59.  Acid  Radical. — An  acid  radical  is  the  acid  minus 
its  replaceable  hydrogen  ;  that  is,  the  radical  for  sulphuric 
acid  is  —  SO4  and  that  of  carbonic  acid  is  —  CO3.     In  case 
only  a  part  of  the  hydrogen  which  the  acid  contains  can  be 
exchanged  for  a  metal,  the  replaceable  hydrogen  should  be 
indicated  in  the  formula.     For  example,  the  formula  for 
tartaric  acid  is  written  H2(C4H4O6)  to  show  that  two  of 
the  six  hydrogen  atoms  which  the  molecule  contains  can 
be   replaced   by   a  metal,  and    that   the    remaining   four 
hydrogen  atoms  form  a  part  of  the  acid  radical.     Since 
each  hydrogen  atom  has  a  valence  of  one,  the  acid  radical 
has  a  valence  equal  to  the  number  of  hydrogen  atoms  with 
which  it  unites. 


ACID   AND  BASIC   SALTS  61 

As  soon  as  the  student  has  learned  the  valences  of  the 
metals,  the  formulas  for  the  -ic  acids,  and  the  rules  for 
naming  acids  and  salts,  the  writing  of  the  formula  for  any 
common  salt  becomes  simple.  The  molecule  is  electrically 
neutral.  It  may  be  looked  upon  as  formed  by  the  com- 
bination of  one  part,  carrying  a  definite  number  of  positive 
charges,  with  another  part,  carrying  an  equal-  number  of 
negative  charges.  For  example,  consider  the  sodium  salt 
of  nitric  acid.  The  formula  for  nitric  acid  is  HNO3. 
Evidently  the  acid  radical  —  NO3  lias  a  valence  of  one  and 
makes  up  the  negative  part  of  the  molecule.  The  valence 
of  potassium  is  one,  and  potassium  is  a  positive  element. 
The  K+  would  unite  with  the  NOq~  to  form  KNO«.  Since 

o  o 

the  salt  is  derived  from  an  acid  containing  oxygen  and 
having  a  name  ending  in  -ic,  the  salt  would  have  a 
name  ending  in  -ate,  that  is,  it  is  a  nitrate.  The  metal 
contained  in  the  salt  is  potassium,  therefore  the  salt 
is  a  potassium  salt  and  the  full  name  of  it  is  potassium 
nitrate. 

Mercury  in  mercuric  compounds  has  a  valence  of  two 
(Hg++).  It  is  evident  from  what  has  already  been  said 
that  two  NO8~  groups  would  unite  with  one  Hg++  group 
and  that  the  formula  for  mercuric  nitrate  would  be 
Hg(NO3)2.  The  normal  salt  derived  from  Ca++  and 
HgPO4  would  be  calcium  phosphate,  Ca3(PO4)2.  The 
formula  for  potassium  tartrate  would  be  K2(C4H4O6)  and 
that  of  sodium  carbonate  is  Na2CO3. 

60.  Acid  and  Basic  Salts.  —  In  addition  to  normal  salts, 
formed  by  exchanging  all  the  replaceable  hydrogen  of  an 
acid  for  a  metal,  acid  and  basic  salts  are  known.  An 
acid  salt  is  formed  when  only  a  part  of  the  replaceable 
hydrogen  of  an  acid  molecule  is  exchanged  for  a  metal. 
Thus  we  have  KHSO4,  potassium  acid  sulphate,  and 


62  NOMENCLATURE  AND    VALENCE 

KH(C4H4O6),  as  illustrations  of  an  acid  salt  of  sulphuric 
acid  and  tartaric  acid  respectively. 

A  basic  salt  is  formed  when  only  a  part  of  the  hydroxyl 
(OH)  of  a  base  is  exchanged  for  an  acid  radical.  Thus 
from  the  base  bismuth  hydroxide,  Bi(OH)3,  and  nitric 
acid  we  may  have  basic  bismuth  nitrate,  Bi(OH)2NOg. 


SUMMARY 

A  Radical  is  a  group  of  elements  which  tend  to  cling  together 
during  a  chemical  change.  Radicals  generally  remain  unaltered 
during  chemical  reactions. 

Valence  is  the  combining  power  of  1  atom  of  an  element  or 
the  combining  power  of  a  radical,  compared  with  the  combining 
power  of  1  atom  of  hydrogen. 

Positive  and  Negative  Elements.  —  Bodies  charged  with  opposite 
kinds  of  electricity  attract  each  other.  Positive  elements  and 
radicals  are  those  which,  on  the  electrolysis  of  their  compounds, 
appear  at  the  negative  electrode  (cathode).  The  terms  positive 
and  negative  are  relative.  The  elements  may  be  arranged  in  an 
electrochemical  series  (page  59)  so  that  each  of  the  elements 
will  be  positive  to  all  elements  above  it,  and  negative  to  all  appear- 
ing in  the  table  below  it.  The  following  table  of  valences  is 
likely  to  be  of  service  to  the  beginner  : 


HYDROGEN  MAGNESIUM  ALUMINUM 

AMMONIUM  (NH4)  CALCIUM  CHROMIUM 

SODIUM  IRON  (in  ferrous  IRON  (in  ferric  com- 

POTASSIUM  compounds)  pounds) 

COPPER  (in  cuprous  COPPER    (in    cupric 

compounds)  compounds) 

SILVER  ZINC 

MERCURY  (in   mer-  BARIUM 

curous  compounds)  MERCURY  (in  mer- 
curic compounds) 


SALTS  63 


HYDROXYL (OH)  OXYGEN  CARBON 

FLUORINE  SULPHUR  SILICON 

CHLORINE  • 

BROMINE 
IODINE 

RULES  FOR  NAMING  INORGANIC   COMPOUNDS 

Binary  Compounds.  —  The  name  of  an  inorganic  compound  con- 
sists of  two  parts.  The  first  part  is  either  the  name  of  the  positive 
element  or  is  derived  from  it.  The  ending  -ous  applied  to  the  first 
part  of  the  name  indicates  that  the  valence  of  the  positive  element 
is  less  than  it  is  when  the  ending  -ic  is  used.  In  binary  compounds, 
the  second  part  is  formed  by  adding  -ide  to  a  root  derived  from  the 
name  of  the  negative  element.  The  prefixes  mono-,  di-t  tri-, 
tetra-,  etc.  are  often  used  to  indicate  the  number  of  negative 
atoms  ip  the  molecule. 

A  Base  is  the  hydroxide  of  a  metal  or  of  a  metallic  radical.  The 
name  of  a  base  consists  of  the  name  of  the  metallic  element  or 
radical  followed  by  the  word  hydroxide. 

Acids.  —  The  rules  for  naming  the  acids  belonging  to  the  same 
series  may  be  indicated  as  follows : 

Hydrochloric  acid     HC1  Molecule  contains  no  oxygen 

Hypochlorous  acid   HC1O  1    less    atom    of    oxygen    than 

chlorous  acid 
Chlorous  acid  HC1O2  1    less    atom    of    oxygen    than 

chloric  acid 

Chloric  acid  HC103  STARTING  POINT 

Perchloric  HC104  1     more    atom   of   oxygen   than 

chloric  acid 

Salts.  —  An  acid  radical  may  be  regarded  as  an  acid  minus  its 
replaceable  hydrogen.  An  acid  and  its  salts  contain  the  same 
radical.  Salts  of  acids  that  contain  oxygen  and  have  names 
ending  in  -ic  are  given  names  ending  in  -ate.  Salts  of  acids  ending 
in  -ous  have  names  ending  in  -ite.  Salts  of  acids  that  contain  no 


64  NOMENCLATURE  AND    VALENCE 

oxygen  have  names  ending  in  -ide.     They  follow  the  rules  for  binary 

compounds. 

ACID  SODIUM  SALT 

Hydrochloric   acid  HC1  Sodium  chloride  NaCl 

Hypochlorous  acid  HC10  Sodium  hypochlorite  NaCIO 

Chlorous          acid  HC102  Sodium  chlorite  NaClCX 

Chloric  acid  HC1O3  Sodium  chlorate  NaClO3 

Perchloric       acid  HC1O4  Sodium  perchlorate  NaClO4 

EXERCISES 

1.  Of  what  value  is  a  knowledge  of  valence  and  the  rules 
of  nomenclature  ? 

2.  What  is  a  binary  compound  ? 

3.  Give  the  general  rules  for  naming  binary  compounds. 

4.  Define  valence. 

5.  The  valence  of  magnesium  is  2.     Write  the  formula  for 
magnesium  oxide. 

6.  Aluminum  has  a  valence  of  3.     What  is  the  formula 
for  aluminum  oxide  ? 

7.  Give  the  chemical  names  of  the  compounds  represented 
by  the  following  formulas:    H2O,  H202,   NaCl,    CaCl2,  FeO, 
Fe2O3,  CC14,  CO,.  C02,  Mn02. 

8.  Write  the  formulas  for  the  following  compounds :  po- 
tassium bromide,  zinc  sulphide,  cuprous  oxide,  cupric  oxide, 
ferrous   chloride,   ferric    chloride,    ferric  sulphate,    aluminum 
sulphate,  ammonium  sulphide,  aluminum  hydroxide. 

9.  What  is  a  base  ?     Give  the  names  and  formulas  of  five 
bases. 

10.  Write   the   formulas   of   the   following:    chloric   acid, 
nitric  acid,  sulphuric  acid,  carbonic  acid,  phosphoric  acid. 

11.  State  the  general  rules  for  naming  acids. 

12.  Why  is  it  unnecessary  to  commit  to  memory  the  va- 
lence of  an  acid  radical  ? 


EXERCISES  65 

13.  What  are  the  formulas  for  the  following :    nitrous  acid, 
hypophosphorous  acid,  sulphurous  acid,  hydrosulphuric  acid, 
perchloric  acid  ? 

14.  How  does  the  formula  for  a  salt  differ  from  that  of  the 
corresponding  acid  ? 

15.  Give  the  general  rules  for  naming  salts. 

16.  PbCr04  is  the  formula  for  lead  chrornate.     What  is  the 
formula  for  chromic  acid?     What  is  the  valence  of  the  radical 
Cr04? 

17.  NaI04  is  the  formula  for  sodium  periodate.     What  is 
the  formula  for  iodic  acid  ? 

18.  What  is  the  formula  for  calcium  hypochlorite  ? 

19.  The   formula   for    acetic    acid    is    sometimes   written 
H(C2H302)  to  show  that  one  molecule  of  the  acid  contains  one 
atom  of  replaceable  hydrogen,  and  that  the  acid  radical   is 
C2H302.     What  is  the  formula  for  lead  acetate  ? 

20.  The  formula  for  tartaric  acid  is  H2(C4H406).     What  is 
the  formula  for  potassium  hydrogen  tartrate  ? 


CHAPTER   VIII 

THE  WRITING  OF  CHEMICAL  EQUATIONS 

61.  Basis  of  Chemical  Equations.  —  It  is  difficult  to  get 
the  beginner  to  realize  that  true  chemical  equations  are 
based   on   results   actually   obtained    in    the   laboratory. 
After  a  large  number  of  cases  have  been  examined,  certain 
principles  governing  chemical  reactions  may  be  discovered, 
but  the  factors  which  enter  the  reaction  may  be  so  many 
that  it  is  impossible  for  the  inexperienced  student  to  pre- 
dict with  certainty  what  change  will  take  place.     Before 
any  chemical  equation  can  be  correctly  written,  the  chem- 
ical change  that  actually  takes  place  must  be  known.    The 
chemical  changes  commonly  met  with  in  elementary  chem- 
istry are  direct  decomposition,  direct  combination,  simple 
replacement,  and  double  replacement. 

62.  Direct  Decomposition  is  the  separation  of  one  com- 
pound into  two  or  more  substances.     Two  illustrations  of 
this  class  of  chemical  change  are  the  decomposition  of 
water  by  electrolysis  and  the  separation  of  mercuric  oxide, 
when  heated,  into  mercury  and  oxygen.     Let  us  consider 
the   writing   of   the   equations   used   to   represent   these 
changes. 

The  student  is  supposed  to  know  that  the  valence  of 
mercury  in  mercuric  compounds  is  2,  that  the  valence  of 
oxygen  is  2,  and  that,  therefore,  the  formula  for  mer- 
curic oxide  is  HgO.  He  has  seen  that  mercuric  oxide, 
on  being  heated,  decomposes  into  mercury  and  oxygen. 
He  is  therefore  at  liberty  to  write  the  chemical 

66 


DIRECT  DECOMPOSITION  67 

equation  representing  the  change  :  HgO  — >-  Hg  +  O. 
But  chemists  recognize  three  kinds  of  oxygen  ;  nascent 
oxygen,  ordinary  oxygen,  and  ozone.  Nascent  oxygen  is 
considered  to  be  atomic  oxygen  (oxygen  as  it  occurs  at 
the  instant  it  is  liberated  from  a  chemical  compound). 
Ordinary  oxygen  is  believed  to  be  composed  of  molecules 
each  of  which  contains  2  atoms.  Ozone  is  thought  to  be 
made  of  molecules  each  containing  3  atoms  of  oxygen. 
Now,  the  oxygen  that  the  student  obtained  when  he  de- 
composed mercuric  oxide  was  ordinary  oxygen.  To  show 
this  fact,  O2  should  take  the  place  of  O  in  the  equation. 
As  the  number  of  atoms  of  mercury  in  a  molecule  of  liquid 
mercury  is  not  known,  the  simplest  number  is  assumed  to 
be  correct,  so  Hg  is  used  to  represent  a  molecule  as  well 
as  an  atom  of  mercury.  The  equation  would  then  become 
HgO  — >-  Hg  +  O2.  But  this  is  not  a  true  equation  be- 
cause it  represents  the  creation  of  an  additional  atom  of 
oxygen,  or  in  other  words,  the  equation  is  not  balanced. 
As  the  composition  of  the  molecules  cannot  be  changed 
without  changing  the  kinds  of  matter  to  be  represented, 
the  number  of  molecules  must  be  made  such  that  the  num- 
ber of  atoms  of  any  element  on  one  side  of  the  equation 
will  equal  the  number  of  atoms  of  that  element  on  the 
other  side  of  the  equation.  This  is  accomplished  by  the 
use  of  coefficients  and  the  equation  is  made  to  read  : 

2HgO-^2Hg  +  02 

mercury  mercury       oxygen 

oxide 

In  writing  the  equation  representing  the  decomposition 
of  water,  the  formula  for  a  molecule  of  water,  and  the 
formulas  for  molecules  of  the  products  may  first  be  written 
H2O  — >•  H2  •+-  O2,  and  the  equation  then  balanced  by  the 
use  of  the  right  coefficients  : 


68        THE    WRITING    OF   CHEMICAL   EQUATIONS 


water  hydrogen     oxygen 

Molecules  of  the  elementary  gases  hydrogen,  chlorine, 
oxygen,  and  nitrogen  each  contain  two  atoms.  Phos- 
phorus and  arsenic  in  gaseous  form  are  composed  of  mole- 
cules containing  four  atoms  each.  The  formulas  for 
molecules  of  these  elements  are  sometimes  written  P4  and 
As4.  Some  elements  in  the  form  of  a  gas,  for  example, 
mercury  and  sodium,  are  made  up  of  molecules  each  hav- 
ing a  mass  equal  to  that  of  the  atom  (Hg  and  Na). 

Sometimes  chemical  decomposition  takes  place,  during 
which  one  compound  is  made  to  yield  two  compounds. 
For  example,  all  common  carbonates,  with  the  exception 
of  those  of  sodium  and  potassium,  when  heated  break  up 
before  they  melt,  yielding  carbon  dioxide  and  a  metallic 
oxide.  Thus  calcium  carbonate,  when  heated  to  a  high 
temperature,  yields  carbon  dioxide  and  calcium  oxide: 

CaO 


calcium  carbon        calcium 

carbonate  dioxide          oxide 

63.  Direct  Combination.  —  Equations  representing  cases 
of  direct  combination  usually  involve  the  chemical  union 
of  two  elements,  but  also  include  the  union  of  molecules  of 
two  compounds.  A  few  examples  may  make  clear  the 
meaning  of  this  statement.  Oxygen  having  a  valence  of 
2,  enters  into  direct  combination  with  carbon,  having  a 
valence  of  4,  to  form  carbon  dioxide  : 

C  +  O2  —  •»-  CO2 

carbon    oxygen         carbon 
dioxide 

Copper  unites  with  sulphur  to  form  copper  sulphide  : 
Cu   +   S  —  >•  CuS 

copper    sulphur        copper 
sulphide 


SIMPLE  REPLACEMENT  69 

Molecules  of  copper  sulphate  enter  into  direct  combi- 
nation with  molecules  of  water  to  form  crystallized  copper 
sulphate : 

CuSO4  +  5  H2O  — >•  CuSO4  -  5  H2O 

copper  water  crystallized 

sulphate  copper  sulphate 

Frequently  an  acid  anhydride  (an  acid  minus  water)  when 
fused  with  a  basic  anhydride  (a  base  minus  water)  will 
combine  to  form  a  salt.  For  example,  calcium  silicate 
may  be  obtained  by  fusing  together  calcium  oxide  (the 
anhydride  of  calcium  hydroxide)  and  silicon  dioxide  (the 
anhydride  of  silicic  acid) : 

CaO  +  SiO2  — >•  CaSiO3 

calcium        silicon  calcium 

oxide          dioxide  silicate 

64.  Simple  Replacement.  —  Cases  of  simple  replacement 
are  frequently  met  with  in  the  laboratory.  The  replace- 
ment of  the  hydrogen  of  an  acid  by  a  metal,  the  decom- 
position of  water  by  a  metal,  the  replacement  of  a  combined 
metal  by  a  free  metal,  and  the  replacement  of  one  non- 
metallic  element  by  another  non-metallic  element  come 
under  this  head. 

The  atom  of  zinc  has  a  valence  of  2.  A  molecule  of 
hydrochloric  acid  contains  one  atom  of  replaceable  hydro- 
gen. Therefore  1  atom  of  zinc,  when  it  reacts  with  hy- 
drochloric acid,  takes  the  place  of  the  hydrogen  in  2 
molecules  of  hydrochloric  acid  : 

Zn  +    2HC1      — ^    ZnCl2    +     H2 

zinc         hydrochloric  zinc  hydrogen 

acid  chloride 

The  student  should  remember  that  every  metal  cannot 
directly  replace  the  hydrogen  of  every  acid.  In  many 
instances,  the  acid  does  not  react  with  the  metal,  and  in  many 


70        THE    WRITING   OF  CHEMICAL   EQUATIONS 

other  cases,  a  secondary  reaction  takes  place,  during  which 
some  of  the  acid  molecules  lose  oxygen,  which  converts 
the  replaced  hydrogen  into  water. 

Other  illustrations  of   simple  replacement   are    repre- 
sented by  the  equations  : 

2  Na  +  2  HOH  —  >-  2  NaOH    +    H2 

sodium  water  sodium          hydrogen 

hydroxide 

Ag2SO4  +   Cu    —  >-  CuSO4    4-   2  Ag 

silver  copper  copper  silver 

sulphate  sulphate 


2KBr    +    C12    —  ^2KC1      +      Br2 

potassium        chlorine  potassium  bromine 

bromide  chloride 

65.  Double  Replacement  is  the  reaction  of  most  com- 
mon occurrence  in  chemistry.  During  double  replacement, 
the  positive  part  of  one  molecule  exchanges  place  with  the 
positive  part  of  another  molecule.  This  exchange  of  place 
is  due  to  the  formation  of  water  (cases  of  neutralization)  ; 
of  a  gaseous  compound,  or  a  compound  which  will  decom- 
pose under  the  conditions  of  the  experiment  so  as  to  yield 
a  gas  ;  or  of  an  insoluble  compound. 

In  cases  of  neutralization,  the  positive  hydrogen  of  the 
acid  combines  with  the  negative  hydroxyl  of  the  base  to 
form  water.  The  components  of  a  salt  are  left  in  solution, 
and  the  salt  generally  separates  on  evaporation  of  the 
liquid.  For  complete  neutralization,  there  must  be  pres- 
ent for  every  acid  hydrogen  atom  a  basic  hydroxyl  radical. 

HCl    +    NaOH   —v  HOH  +  NaCl 

hydrochloric          sodium  water  sodium 

acid  hydroxide  chloride 

H2S04  +  2  KOH  —  >-  2  HOH  +  K2SO4 

sulphuric         potassium  water  potassium 

acid  hydroxide  sulphate 


DOUBLE  REPLACEMENT  71 

In  the  last  equation,  since  every  sulphuric  acid  molecule 
contains  two  acid  hydrogen  atoms,  two  molecules  of 
potassium  hydroxide  must  be  taken  in  order  to  furnish 
the  necessary  number  of  hydroxyl  groups.  The  following 
equations  represent  other  instances  of  neutralization  : 

Ca(OH)2    +  2  HNO3   — >-  2  HOH  4-  Ca(NO3)2 

calcium  nitric  water  calcium 

hydroxide  acid  nitrate 

2  A1(OH)3  +  3  H2S04  —+•  6  HOH  +  A12(SO4)3 

aluminum  sulphuric  water  aluminum 

hydroxide  acid  sulphate 

Instances  in  which  double  replacement  is  due  to  the 
formation  of  a  gaseous  compound  may  be  illustrated  by 
the  reaction  between  sulphuric  acid  and  the  salt  of  an 
acid  having  a  lower  boiling  point.  When  sulphuric  acid 
is  added  to  potassium  nitrate  for  the  purpose  of  making 
nitric  acid,  the  temperature  is  so  regulated  that  it  will  be  a 
little  above  the  boiling  point  of  nitric  acid  and  far  below 
that  of  sulphuric  acid.  Under  these  conditions,  the  nitric 
acid  as  soon  as  it  is  formed  escapes  as  a  gas  from  the  re- 
acting mass : 

2  NaN03  +  H2S04  —*-  2  HNO3  +  Na2SO4 

sodium  sulphuric  nitric  sodium 

nitrate  acid  acid  sulphate 

Ammonium  hydroxide,  carbonic  acid,  and  sulphurous 
acid  are  examples  of  compounds  that  readily  decompose, 
yielding  a  gas  as  one  of  the  products  of  decomposition. 
When  nitric  acid  is  added  to  calcium  carbonate,  the  car- 
bonic acid  formed  at  once  decomposes  into  water  and  the 
gas  carbon  dioxide  : 


72        THE    WRITING   OF   CHEMICAL  EQUATIONS 
CaCOg  +  2  HNO3  —  >-  Ca(NO3)2  +  H2CO3 

calcium  nitric  calcium  carbonic 

carbonate  acid  nitrate  acid 

H2C03  —  >-  H20  +  C02 

carbonic  water        carbon 

acid  dioxide 

These  two  equations  are  usually  combined  into  one  : 
CaC03+2HN03—  ^Ca(N03)2+H20  +  CO2 

calcium  nitric  calcium  water         carbon 

carbonate  acid  nitrate  dioxide 

In  a  similar  manner,  when  an  ammonium  salt  is  heated 
with  a  non-volatile  base,  double  replacement  takes  place, 
because  as  soon  as  the  ammonium  hydroxide  is  formed,  it 
decomposes,  yielding  the  gas  ammonia,  and  water  : 


2NH4C1- 

ammonium 
chloride 

f-  Ca(OH)2 

calcium 
hydroxide 

—  »-  CaCl2  4 

calcium 
chloride 

-2NH4OH 

ammonium 
hydroxide 

2NH4OH 

ammonium 
hydroxide 

—  >-  2  NH3  4 

ammonia 

-2H2O 

water 

The  final  equation,  representing  the  completed  reaction,  is  : 
2  NH4C1  +  Ca(OH)2  —  »-  CaCl2  +  2  NH3  +  2  H2O 

ammonium  calcium  calcium         ammonia          water 

chloride  hydroxide  chloride 

Instances  in  which  double  replacement  is  due  to  the 
formation  of  an  insoluble  compound  are  very  common  ;  in 
fact,  a  large  portion  of  the  reactions  used  in  analytical 
chemistry  are  double  replacements.  The  formation  of  in- 
soluble silver  chloride,  on  the  addition  of  a  solution  of 
silver  nitrate  to  a  solution  of  a  soluble  chloride,  and  the 
formation  of  insoluble  barium  sulphate,  on  the  addition  of 
a  solution  of  barium  chloride  to  a  solution  of  a  sulphate, 
are  common  examples  : 


SUMMARY  73 

NaCl  +  AgNO3  — ^  AgCl  +  NaNO8 

sodium  silver  silver  sodium 

chloride          nitrate  chloride          nitrate 

Na2SO4  +  BaCl2  — >-  BaSO4  +  2  NaCl 

sodium  barium  barium  sodium 

sulphate          chloride  sulphate          chloride 


SUMMARY 

Direct  Decomposition  is  the  breaking  of  a  compound  into  two  or 
more  substances  by  the  application  of  some  form  of  energy. 

Direct  Combination  is  the  formation  of  one  compound  from  two 
or  more  substances. 

Simple  Replacement  is  the  exchange  of  place  between  a  com- 
bined and  a  free  element. 

Double  Replacement  is  the  exchange  of  place  between  the  pos- 
itive part  of  one  molecule  and  the  positive  part  of  another  mole- 
cule. Double  replacement  is  generally  due  to  one  of  the 
following : 

(#)  neutralization, 

(b~)  formation  of  a  volatile  compound, 

(c)  formation  of  an  insoluble  compound. 

The  Writing  of  Chemical  Formulas  involves  a  knowledge  of  the 
symbols  and  the  valences  of  the  elements,  and  an  understanding 
of  the  rules  of  nomenclature. 

Chemical  Equations  are  based  upon  data  obtained  in  the  labora- 
tory. Before  a  true  chemical  equation  can  be  written,  the 
chemical  change,  or  changes,  that  actually  take  place  must  be 
known.  This  implies  a  knowledge  of  the  composition  of  the  ini- 
tial substances  and  of  the  products  formed.  The  student  must 
also  understand  how  to  use  coefficients,  so  that  the  same  weight 
of  matter  will  be  represented  by  each  side  of  the  equation. 


74       THE    WRITING   OF  CHEMICAL  EQUATIONS 


EXERCISES 

1.  What  must  be  known  before  a  true  chemical  equation 
can  be  written  ? 

2.  What  are  the  steps  to  be  followed  in  writing  a  chemical 
equation  ? 

3.  What  is  the  meaning  of  the  term  "  direct  decomposition  "  ? 

4.  Mention  two  cases  of  direct  decomposition  that  you 
have  studied,  and  write  the  chemical  equations  representing 
them. 

5.  Why  should  ordinary  oxygen   be  represented   by  the 
formula  02  and  not  by  the  symbol  0  ? 

6.  Magnesium  carbonate,  on  being  heated,  yields  carbon 
dioxide  and  magnesium  oxide.     Write  the   chemical  equation 
representing  this  change. 

7.  Define  direct  combination. 

8.  Mention  five  illustrations  of   direct  combination,  and 
write  chemical  equations  to  represent  the  changes  taking  place. 

9.  What  is  an  acid  anhydride  ?     A  basic  anhydride  ? 

10.  What  kind  of  a  compound  is  formed  when  an  acid  anhy- 
dride combines  with  a  basic  anhydride  ? 

11.  What  is  the  meaning  of  the  formula  CuS04 .  5  H20  ? 

12.  W^hat  is  meant  by  "  simple  replacement "  ? 

13.  When  a  needle  is  placed  in  a  solution  of  copper  sul- 
phate, it  becomes  coated  with  copper.     Represent  by  an  equa- 
tion the  chemical  change  that  takes  place. 

14.  Define  "double  replacement." 

15.  Name  three  conditions  permitting  double  replacement 
to  proceed. 

16.  Write  the  equation  for  the  neutralization  of  ammonium 
hydroxide  by  sulphuric  acid. 


EXERCISES  75 

17.  Silver  chloride  is  insoluble  in  water.     Silver  nitrate  is 
soluble.     What  chemical  reaction  occurs  when  a  solution   of 
sodium  chloride   is   added   to   a   solution   of   silver    nitrate  ? 
Equation  ? 

18.  Hydrogen   chloride  is  a  gas.     Sulphuric  acid  boils  at 
338°  C.    Sodium  sulphate  is  a  solid.    What  would  be  the  result 
of  heating  sodium  chloride  with  sulphuric  acid  ?    .Equation  ? 

19.  Ammonium  hydroxide  is  unstable  and  readily  decom- 
poses, yielding  water  and  the  gas  ammonia  (NH3).     What  gas 
would  be  formed  when  an  ammonium  salt  was  treated  with  a 
non-volatile  base  ? 

20.  Write  the  equation  for  the  reaction  between  ammonium 
sulphate  and  calcium  hydroxide. 


NOTE  TO  INSTRUCTORS.  —  Instructors  who  may  wish,  after  finish- 
ing this  chapter,  to  give  some  work  on  chemical  calculations  will  find 
ample  material  in  Chapter  XLVI,  and  may  select  the  types  of  calcu- 
lations desirable  for  their  classes.  The  authors,  however,  believe  that 
the  greater  number  of  instructors  will  take  up  directly  the  chapters 
immediately  following  this,  which  deal  with  more  practical  affairs  of 
life. 


CHAPTER   IX 

SOLUTIONS 

66.  Nature  of  Solutions.  —  When  a  spoonful  of  common 
salt  is  placed  in  a  tumbler  of  water,  the  salt  gradually  dis- 
appears. The  result  is  a  clear,  transparent  liquid,  any 
portion  of  which  has  a  salty  taste.  Not  only  has  the  salt 
gone  into  the  water,  but  it  has  penetrated  every  portion 
of  it.  Just  how  the  process  occurs  is  beyond  the  power 
of  our  eyes  to  see.  We  know,  however,  thai  the  finer  the 
salt  is  powdered,  the  quicker  it  will  go  into  the  water  or 
dissolve.  These  facts  lead  us  to  think  that  extremely  fine 
particles  separate  from  the  grains  of  salt  and  mix  with  the 
water  particles,  which  are  too  minute  to  be  seen.  In  this 
manner  a  solution  of  salt  and  water  is  obtained  which  has 
the  remarkable  property  of  being  alike  in  every  portion, 
not  only  as  to  color,  transparency,  and  taste,  but  in  con- 
taining the  same  amount  of  water  and  salt  in  every  cubic 
centimeter,  provided  the  solution  has  been  thoroughly 
stirred.  Thus  the  salt  solution  is  a  mixture  of  uniform 
composition. 

All  compounds  have  one  property  in  common  —  uni- 
formity of  composition.  Compounds  are  formed  by  ele- 
ments combining  in  certain  definite  proportions  by  weight. 
At  the  first  glance  it  seems  as  if  our  salt  solution  followed 
the  law  of  definite  proportions,  and  is  therefore  a  chemical 
compound.  But  any  compound  has  always  the  same 
weight  composition  however  it  is  made.  If  we  had  put 
half  a  spoonful  of  salt  into  our  tumbler  of  water,  another 

76 


SOLUBLE  AND   INSOLUBLE   SUBSTANCES         77 

uniform  mixture  of  salt  and  water  would  have  been  ob- 
tained, but  the  second  mixture  would  not  have  the  same 
composition  as  the  first.  In  fact  many  such  uniform  mix- 
tures may  be  made  by  varying  the  relative  quantities  of 
salt  and  water.  Hence  it  is  seen  that  there  is  no  one 
definite  composition  for  salt  solutions,  and  that  any  such 
mixture,  no  matter  how  uniform  its  composition  may  be, 
cannot  properly  be  classed  as  a  chemical  compound.  A 
solution  is  a  mixture  of  uniform  composition  which  does  not 
follow  the  law  of  definite  proportions. 

67.  Solvent  and  Solute.  —  A  substance  like  water,  which 
has  the  power  of  dissolving  another  substance,  is  known  as 
a  solvent.     The  substance  dissolved  is  termed  the  solute. 
Although  in  some  instances  solids  and  gases  act  as  solvents, 
liquids  are  the  solvents  of  greatest  practical  importance. 
Water,  alcohol,  benzine,  chloroform,  and  ether  are  some  of 
the  liquid  solvents  much  employed.     Although  water  is 
the  solvent  of  common  household  use,  other  solvents  are 
found  necessary  for  the  preparation    of   medicines,  var- 
nishes, and  other  commercial  products.     The  most  desir- 
able solvent  for  a  particular  substance  has  to  be  determined 
by  experiment.      A  knowledge  of  the  general  behavior  of 
solvents  may  best  be   acquired   by   the  study    of   water 
solutions. 

68.  Soluble   and  Insoluble  Substances.  —  Sugar  and  salt 
are  familiar  substances  that  dissolve  without  difficulty  in 
water,  and  are  known  therefore  as  substances  soluble  in 
water.      Sand,  sulphur,  silver,  iron,  wood,  and  many  other 
materials  when  placed  in  water  do  not  dissolve.     They 
either  settle  to  the  bottom  or  float  on  the  liquid.     Such 
substances  are  said  to  be  insoluble  in  water.     Hot  water 
poured  on  tea  leaves  gives  a  clear  yellowish  liquid,  show- 


78  SOLUTIONS 

ing  that  at  least  one  of  the  substances  in  the  tea  leaves  is 
soluble.  Though  the  process  may  be  repeated  a  large 
number  of  times,  insoluble  substances  still  remain. 

The  solvent  action  of  water  aids  in  the  disintegration 
of  rocks  by  taking  out  the  soluble  substances  formed  in 
processes  of  weathering.  The  value  of  marble,  sandstone, 
and  slate  as  building  materials  rests  in  part  on  their  prac- 
tical insolubility  in  water. 

The  muddy  waters  of  brooks  and  rivers  in  spring  con- 
tain substances  in  solution,  but  owe  their  turbidity  to 
numberless  fine  particles  of  insoluble  solids  held  in  sus- 
pension. While  a  suspension  at  a  given  moment  may  have 
a  rather  uniform  distribution  of  the  solid  particles,  it 
differs  from  a  solution  in  that  the  solid  particles  will 
separate  eventually  from  the  liquid,  usually  settling  to  the 
bottom.  As  long  as  the  conditions  affecting  a  solution 
remain  unchanged,  the  dissolved  particles  remain  uni- 
formly distributed  throughout  the  solvent. 

69.  Dilute  and  Concentrated  Solutions.  —  Rain  water 
always  contains  a  very  small  amount  of  dissolved  matter. 
Such  a  solution,  consisting  of  a  relatively  large  amount  of 
the  solvent  to  a  small  amount  of  the  dissolved  substance 
(solute),  is  a  dilute  solution.  Brook  and  river  waters  are 
also  dilute  solutions,  but  contain  a  rather  larger  amount 
of  dissolved  matter  than  rain  water.  This  additional 
matter  is  obtained  from  the  soil.  The  growth  and  life  of 
plants  depends  upon  the  sap,  a  dilute  solution  containing 
mineral  substances  taken  in  through  the  roots,  and  upon 
food  materials  made  in  the  leaves.  Most  beverages  con- 
tain but  small  amounts  of  the  dissolved  substances  in  large 
amounts  of  the  solvent,  usually  water.  Vinegar  is  mainly 
a  very  dilute  solution  (4  %)  of  acetic  acid.  Most  medi- 
cines in  liquid  form  are  dilute  solutions  of  various  drugs. 


DILUTE  AND   CONCENTRATED   SOLUTIONS       79 

In  very  dilute  solutions,  the  particles  of  the  dissolved 
substances  are  widely  separated  from  each  other  by  large 
quantities  of  the  solvent.  When  a  dilute  water  solution 
of  sugar  is  heated,  some  of  the  water  evaporates.  As  this 
process  continues,  some  of  the  dissolved  particles  of  sugar 
are  brought  closer  together  or  concentrated  in  a  smaller 
volume.  In  this  manner,  a  concentrated  solution  of  sugar 
may  be  obtained.  Even  if  the  dilute  sugar  solution  was 
allowed  to  stand  at  the  ordinary  temperature,  the  slow 
evaporation  of  the  water  would  give  a  concentrated  solu- 
tion. Concentrated  solutions  differ  from  dilute  solutions 
in  containing  a  much  larger  amount  of  dissolved  substance 
in  proportion  to  the  amount  of  the  solvent.  Often  it  is 
more  desirable  to  prepare  a  concentrated  solution  directly 
by  mixing  solvent  and  solute,  rather  than  by  evaporation 
of  a  dilute  solution.  Thus,  caustic  potash  may  be  dissolved 
in  its  own  weight  of  cold  water  ;  caustic  soda  is  more  solu- 
ble. Zinc  chloride,  used  in  soldering  solutions,  gives  still 
more  concentrated  solutions,  as  it  dissolves  in  half  its 
weight  of  water  at  ordinary  temperatures.  At  higher 
temperatures,  concentrated  solutions  of  some  substances 
may  be  prepared,  in  which  a  given  amount  of  solvent  con- 
tains five  or  six  times  as  much  of  the  dissolved  substance. 

As  has  been  stated,  the  relative  amounts  of  the  solvent 
and  the  solute  determine  whether  a  solution  is  dilute  or 
concentrated.  When  the  amount  of  the  dissolved  sub- 
stance is  comparatively  small,  the  solution  is  dilute ; 
when  the  amount  of  the  solute  is  relatively  large,  the  solu- 
tion is  concentrated.  Like  all  things  depending  upon  two 
variable  factors,  the  two  kinds  of  solution,  dilute  and 
concentrated,  grade  into  each  other.  In  natural  processes, 
dilute  solutions  are  far  more  common  than  concentrated ; 
in  many  manufacturing  operations,  concentrated  solutions 
are  much  employed.  Sometimes,  however,  dilute  solu- 


80  SOLUTIONS 

tions  are  necessary.  For  the  laboratory,  concentrated 
solutions  are  the  most  convenient  form  to  keep  on  hand. 
From  them  dilute  solutions  can  readily  be  made  by  the 
addition  of  more  of  the  solvent. 

70.  Saturated  Solutions.  —  Experiments  with  dilute  and 
concentrated  solutions  show  that  the  solubility  of  a  sub- 
stance in  a  certain  solvent  has  its  limits.  Pure  salt, 
sodium  chloride,  added  to  cold  water  in  small  amounts 
slowly  dissolves.  Soon,  however,  the  last  portion  of  the 
salt  remains  undissolved,  no  matter  how  finely  it  may  be 
powdered  or  how  much  the  salt  and  water  are  shaken 
together.  The  given  amount  of  water  has  dissolved  all  of 
the  salt  that  it  can  at  that  temperature.  Such  a  solution, 
in  which  the  solvent  at  a  certain  temperature  has  dissolved 
all  of  a  given  substance  possible,  is  a  saturated  solution  of 
that  substance  under  existing  conditions.  Temperature  is 
the  condition  which  most  affects  the  preparation  of  satu- 
rated solutions. 

It  might  be  thought  that  the  water  in  a  saturated  solu- 
tion of  ammonium  chloride  at  the  room  temperature  had 
reached  the  limit  of  its  dissolving  power  at  that  tempera- 
ture. This  is  true  with  respect  to  the  ammonium  chloride, 
but  not  with  regard  to  other  substances  soluble  in  water. 
For  example,  magnesium  sulphate  will  dissolve  readily 
in  such  a  saturated  solution  of  ammonium  chloride. 
Hence  a  saturated  solution  should  be  defined  with  re- 
spect to  a  particular  substance  as  well  as  to  a  definite 
temperature. 

Solids  differ  greatly  in  the  degree  of  their  solubility  in 
water,  hence  saturated  solutions  of  various  substances  at 
the  ordinary  temperature  contain  widely  differing  amounts 
of  the  dissolved  substances.  Limewater  is  a  saturated 
solution  of  calcium  hydroxide  containing  about  2  parts  by 


SATURATED   SOLUTIONS  81 

weight  of  lime  to  1000  of  water.  A  saturated  solution  of 
boric  acid  contains  about  4  parts  in  100  of  water.  The 
ordinary  sal  ammoniac  solution  used  in  wet  batteries,  con- 
tains about  1  part  of  ammonium  chloride  to  3  parts  of 
water. 

Two  other  highly  important  conditions  in  the  making 
of  concentrated  and  saturated  solutions  are  the  size  of  the 
particles  of  the  substance  to  be  dissolved,  and  the  closeness 
of  contact  of  the  solvent  with  every  particle  of  the  solute. 
Thus  time  is  saved  by  finely  powdering  the  solid.  This  is 
done  in  the  laboratory  with  a  mortar  and  pestle,  while  in 
manufacturing  establishments  grinding  mills  or  rotary 
crushers  are  employed.  In  the  household,  stirring  with  a 
spoon  brings  the  solvent  and  solute  into  close  contact.  In 
the  laboratory,  it  is  customary  to  shake  the  two  together 
in  a  flask  or  test  tube,  or  to  use  a  stirring  rod  in  a  beaker. 
Technical  establishments  prepare  large  quantities  of  solu- 
tions in  vats  in  which  paddles  are  rotated. 


FIG.   16. — RELATIVE   SOLUBILITY   OF  SODIUM  CHLORIDE  IN  COLD  AND  IN 
HOT  WATER. 


82 


SOLUTIONS 


71.  Effect  of  Temperature  on  the  Solubility  of  Solids.  — 
When  a  solution  of  sodium  chloride,  which  was  saturated 
at  20°  C.,  is  heated  without  the  loss  of  water  to  a  higher 
temperature,  it  is  found  that  a  little  more  salt  can  be  dis- 
solved (Fig.  16).  That  is,  the  solution  which  is  satu- 
rated at  20°  C.  is  not  saturated  at  the  higher  temperature. 
The  increase  in  temperature  has  increased  the  solubility 
of  sodium  chloride  in  water.  While  sodium  chloride  is 


FIG.   17. —  RELATIVE   SOLUBILITY   OF   POTASSIUM   NITRATE  IN  COLD  AND  IN 

HOT  WATER. 

but  slightly  more  soluble  in  hot  water  than  in  cold, 
potassium  nitrate  is  about  eight  times  as  soluble  in  boiling 
water  as  in  cold  water  (Fig.  17).  Crystals  of  washing 
soda  are  vastly  more  soluble  in  lukewarm  water  (35°C.) 
than  in  water  at  20°  C.  In  general  the  solubility  of  most 
solids  in  liquids  increases  with  the  temperature. 

72.    Crystallization   and    Precipitation.  —  When   a    satu- 
rated solution  of  a  solid  is  allowed  to  stand,  the  water 


CRYSTALLIZATION  AND  PRECIPITATION         83 

evaporates  in  part.  The  decreased  amount  of  the  solvent 
means  that  some  of  the  dissolved  substance  must  come 
out  of  solution.  Many  of  these  solids  in  so  doing  deposit 
in  crystalline  form.  Often  the  crystals  are  easily  recog- 
nized because  of  their  approximation  to  some  well-known 
geometric  form.  Alum,  for  example,  gives  crystals 
shaped  like  two  four-sided  pyramids  placed  base  to  base, 
which  constitute  an  octahedron  (Fig.  18  «,  apex  of  one 
pyramid  in  foreground).  Sodium  chloride  and  potassium 


FIG.   18. — TYPICAL  CRYSTALS. 
a.  Potassium  Alum  ;  b,  Sodium  Nitrate  ;  c,  Nickel  Sulphate. 

chloride  form  cubical  crystals  similar  to  those  in  Fig.  18  b. 
Rock  candy  consists  simply  of  a  mass  of  sugar  crystals 
whose  form  can  easily  be  seen. 

When  we  mix  a  solution  of  sodium  chloride  with  a 
solution  of  silver  nitrate,  we  obtain  a  white,  cloudy  mix- 
ture. On  standing,  a  white  solid  gradually  settles  to  the 
bottom  of  the  tube.  An  analysis  of  the  solid  shows  that 
it  is  silver  chloride.  This  compound  did  not  exist  in 
either  of  the  two  solutions  that  we  put  together,  but  was 


84 


SOLUTIONS 


formed  on  mixing  them.     A   study  of   the  equation  for 
the  reaction, 

NaCl  +  AgNO3  — >-  AgCl  +  NaNO3 


sodium 
chloride 


silver 
nitrate 


silver 
chloride 


sodium 
nitrate 


shows  that  it  is  one  of  double  replacement.  The  sodium 
and  the  silver  have  exchanged  places,  forming  silver 
chloride  and  sodium  nitrate.  The  latter,  being  readily 
soluble,  remains  dissolved  in  the  water  of  the  two  solu- 
tions which  were  mixed.  Silver  chloride,  the  other 
product,  is  only  slightly  soluble  in  water.  In  fact,  the 
solution  is  saturated  with  respect  to  this  substance  and 
the  extra  amount  formed  by  the  action  of  double  replace- 
ment has  to  fall  out  of  the  solution,  that  is,  it  is  precipi- 
tated. In  this  way  precipitates  are  formed  on  mixing 
solutions  of  two  soluble  substances  which  will  yield  an 

insoluble  product.  Such  pre- 
cipitates may  be  either  crystal- 
line or  amorphous  (lacking  defi- 
nite crystalline  form). 

73.    Miscibility  of   Liquids.  — 

"  Oil  and  water  will  not  mix  " 
is  an  old  way  of  saying  that 
these  two  liquids  do  not  dis- 
solve in  each  other.  If  the  oil 
is  kerosene,  it  floats  on  top  be- 
cause it  is  lighter  than  water. 
Chloroform  is  insoluble  in  water, 
and,  being  heavier,  sinks  to  the 
bottom.  In  both  of  these  cases 
there  is  a  very  distinct  boundary  line  between  the  two 
liquids  (Fig.  19).  When,  however,  grain  alcohol  is 


FIG.  19.  —  NON-MISCIBLE 
LIQUIDS. 


SOLUTION  OF  GASES  85 

poured  into  water  and  the  mixture  shaken,  neither 
liquid  can  be  distinguished.  We  say  that  the  two  liquids 
are  miscible  (i.e.  "mixable").  Each  liquid  is  com- 
pletely soluble  in  the  other.  Carbon  disulphide  and  water 
are  two.  non-miscible  liquids.  An  emulsion  is  a  case  of 
non-miscibility  where  the  particles  of  the  two  liquids  re- 
main intermingled.  Cod-liver  oil  forms  an  emulsion  with 
water.  The  fatty  particles  constituting  the  cream  of  milk 
are  in  a  state  of  emulsion  in  fresh  milk.  Kerosene  emul- 
sion, used  for  killing  plant  lice,  is  made  by  agitating  a 
mixture  of  soap,  water,  and  kerosene. 

Since  two  non-miscible  liquids  form  two  distinct  lay- 
ers, they  may  be  easily  separated  by  drawing  off  one  of 
them.  It  is  very  difficult,  however,  to  separate  two  mis- 
cible liquids,  like  alcohol  and  water,  without  resorting  to 
some  complicated  process,  such  as  fractional  distillation. 

74.  Solution  of  Gases.  —  When  a  glass  of  water,  freshly 
drawn  from  the  tap,  is  allowed  to  stand  at  the  room  tem- 
perature, the  sides  of  the  glass  often  become  coated  with 
bubbles.  These  consist  of  gases  which  have  been  dis- 
solved by  the  water.  The  water  drawn  from  the  faucet 
was  colder  than  the  temperature  of  the  room.  When  the 
water  was  warmed  to  the  room  temperature,  it  could  hold 
less  of  the  dissolved  gases.  Unlike  solids,  the  solubility  of 
a  gas  in  a  liquid  is  lessened  with  an  increase  of  temperature. 
The  solubility  of  a  gas  in  a  liquid  is  usually  expressed  in 
terms  of  volume.  The  table  on  page  86  shows  the  relative 
solubility  of  some  of  the  common  gases  and  the  effect  of 
temperature  on  their  solubility. 

A  few  gases  are  exceedingly  soluble  in  water.  At  the 
ordinary  temperature  1  c.c.  of  water  will  dissolve  700  c.c. 
of  ammonia,  or  nearly  450  c.c.  of  hydrogen  chloride. 
Another  way  of  stating  the  last  fact  is  that  1  volume  of 


86 


SOLUTIONS 


GAB 

NUMBEB  OF  c.c.  DISSOLVED  BY  100  c.c.  OF  WATER  AT 

0°C. 

20°  C. 

100°  C. 

Hydrogen  
Nitrogen  
Oxvsreri  . 

2.15 
2.39 
4.89 
5.56 
171.30 

129890.00 

1.82 
1.64 
3.10 
3.31 
87.80 
226.00 
71060.00 

1.60 
1.00 

1.70 
1.70 

0.00 

Methane  .  ... 

Carbon  dioxide  .... 
Chlorine  
Ammonia  

water  dissolves  450  volumes  of  hydrogen  chloride.     When 
vichy  or   seltzer  is    drawn  from  a   siphon  (Fig.  20)    the 

water  rushes  out  through  the 
valve  with  a  hissing  noise.  In 
the  tumbler,  streams  of  gas 
bubbles  rise  through  the  liquid 
and  break  at  the  surface.  The 
gas  which  escapes  so  violently 
from  the  liquid  is  carbon  di- 
oxide, and  its  pressure  is  greater 
than  that  of  the  air  into  which 
it  escapes.  Evidently  the  pres- 
sure at  which  the  carbon  dioxide 
was  dissolved  in  the  water  was 
much  greater  than  the  atmos- 
pheric pressure.  In  other 
words,  increasing  the  pressure  causes  the  water  to  dissolve 
a  greater  weight  of  carbon  dioxide.  Therefore  it  may  be 
stated  that  the  weight  of  a  gas  dissolved  increases  with  the 
pressure.  Bottled  mineral  waters  or  other  highly  efferves- 
cent beverages  are  charged  with  a  soluble  gas  under  pres- 
sure. Consequently  the  containers  and  stoppers  must  be 
strong.  The  pressure  in  a  siphon  soda  bottle  is  140  pounds 


FIG.  20. 


SUMMARY  87 

per  square  inch  ;  in  ginger  ale  bottles,  90  pounds ;  and  in 
club  soda  bottles,  105  pounds.  On  the  opening  of  the 
bottles,  there  is  always  danger  that  the  sudden  release  of 
pressure  at  the  stopper  will  allow  the  dissolved  gas  to 
rush  out  with  such  force  as  to  burst  a  defective  bottle. 
To  avoid  the  danger  of  flying  glass  in  such  a  case,  it  is 
always  advisable  to  wrap  a  cloth  around  a  bflttle  contain- 
ing a  charged  liquid  before  opening  it. 

SUMMARY 

A  Solution  is  a  mixture  of  uniform  composition  which  does  not 
follow  the  Law  of  Definite  Proportions. 

A  Solvent  is  a  substance  which  has  the  power  of  dissolving 
another  substance. 

A  Solute  is  a  substance  dissolved. 

Turbidity  is  due  to  small  solid  particles  held  in  suspension. 
These  in  time  will  usually  settle  to  the  bottom. 

Dilute  and  Concentrated  are  relative  terms  applied  to  solutions. 
The  greater  the  amount  of  solute  in  comparison  with  the  amount 
of  solvent,  the  more  concentrated  is  the  solution.  Concentrated 
solutions  may  be  prepared  by  evaporating  part  of  the  solvent  from 
the  dilute  solution. 

A  Saturated  Solution  of  a  substance  is  obtained  when  the  sol- 
vent has  dissolved  all  it  can  of  that  substance  under  the  existing 
conditions,  particularly  as  to  temperature. 

The  Solubility  of  Most  Solids  in  liquids  increases  with  the  tem- 
perature. 

Precipitates  are  formed  when  the  mixing  of  the  solutions  of  two 
soluble  substances  yields  an  insoluble  substance. 

Crystallization  is  the  separation  of  a  dissolved  solid  in  definite 
form  and  is  usually  due  to  the  partial  evaporation  of  the  solvent, 
or  to  the  cooling  of  the  solution. 


88  SOLUTIONS 

Miscible  Liquids  are   those  which    are   completely  soluble   in 
each  other. 

Gases  decrease  in  solubility  with  an  increase  in  temperature. 


EXERCISES 

1.  What  are  the  characteristics  of  a  solution  ? 

2.  What  is  the  greatest  difference  between  the  composition 
of  a  compound  and  of  solutions  of  that  compound  ? 

3.  Distinguish  between  solvent  and  solute. 

4.  Name  five  of  the  common  liquid  solvents. 

5.  What  is  the  most  widely  used  solvent  ? 

6.  How  would  you  determine  whether  or  not  a  solid  is  sol- 
uble in  water? 

7.  State  the  difference  between  a  dilute  and  a  concentrated 
water  solution  of  alum. 

8.  How  would  you  prepare  a  saturated  water  solution  of  a 
very  soluble  substance  ?      Of  a  moderately  soluble  substance  ? 

9.  How  could  you  determine  that  the  limewater  sold  in 
drug  stores  is  simply  a  dilute  solution  ? 

10.  Define  a  saturated  solution. 

11.  How  can  you  tell  when  a  solution  is  saturated  with  re- 
spect to  a  particular  substance  ? 

12.  What  is  the  quickest  way  to  make  a  cold  saturated 
solution  of  boric  acid  ? 

13.  What  effect  does  the  temperature  have  upon  the  solubil- 
ity of  most  solids  ? 

14.  Compare   the   relative   solubility  of  common  salt  and 
washing  soda  in  hot  and  in  cold  water. 

15.  How  would  you  obtain  crystals  of  blue  vitriol  from  some 
of  the  finely  powdered  substance  ? 

16.  Describe  a  case  of  precipitation  by  the  action  of  double 
replacement. 


EXERCISES  89 

17.  What  is  meant  when  it  is  said  that  carbon  disulphide 
and  water  are  non-miscible  ? 

18.  Name  two  miscible  liquids.     What  is  an  emulsion  ? 

19.  Account  for  the  bubbles  seen  in  a  glass  of  ginger  ale. 

20.  Compare  the  solubility  of  oxygen  in  hot  and  in  cold 
water.     How  does  the  solubility  of  oxygen  in  water  differ  from 
that  of  carbon  dioxide  ? 

21.  What  advantage  is  taken  of  the  great  solubility  of  am- 
monia for  its  transportation  ?     What  other  gas  is  distributed 
in  a  similar  manner  ? 

22.  Explain  the  dangers  in  handling  bottles  or  siphons  con- 
taining charged  waters. 


Courtesy  of  The  Century  Co. 


FIG.  21.  —  FIGHTING  FIRE. 


90 


CHAPTER   X 
BURNING  AND  OXIDATION 

75.  Burning.  —  When  the  strip  of  copper  was  thrust  into 
the  test  tube  containing  boiling  sulphur,  the  copper  took 
fire  and  burned  in  the  sulphur  vapor  (§8).  A  new  sub- 
stance, copper  sulphide,  was  formed.  In  all  ordinary  cases 
of  burning,  however,  chemical  action  takes  place  between 
the  oxygen  of  the  air  and  the  substance  burned.  Oxides 
result  from  the  chemical  reaction,  because  the  same  sub- 
stance is  formed  when  a  certain  kind  of  matter  is  burned 
in  air  that  is  formed  when  that  kind  of  matter  is  burned 
in  oxygen.  Remove  oxygen  from  air  and  substances  cease 
to  burn.  Sulphur  burns  readily  in  air,  and  the  product  of 
combustion  has  a  characteristic  odor.  When  sulphur  is 
burned  in  pure  oxygen,  a  gas,  sulphur  dioxide,  is  formed 
which  has  the  same  odor  as  the  product  obtained  by  burn- 
ing sulphur  in  air.  Steam,  which  may  be  readily  con- 
densed to  water,  is  formed  when  hydrogen  is  burned  in 
air,  and  also  when  hydrogen  is  burned  in  pure  ox}Tgen. 
Carbon  dioxide,  a  colorless  gas  which  causes  limewater 
to  become  milky,  is  formed  when  carbon  is  burned  in  oxy- 
gen, and  likewise  when  carbon  is  burned  in  air.  If  oxy- 
gen is  removed  from  air,  neither  sulphur,  hydrogen,  nor 
carbon  will  burn  in  the  remaining  gases. 

We  commonly  speak  of  the  gas  in  which  a  substance 
burns  as  being  a  supporter  of  combustion,  and  of  the  sub- 
stance burned  as  being  combustible.  These  terms  are 
simply  convenient  to  use,  for  air  will  burn  as  readily  in 

91 


92  BURNING   AND   OXIDATION 

illuminating  gas  as  illuminating  gas  will  burn  in  air.  Ii 
either  case  the  burning  is  due  to  the  fact  that  the  ilium  i 
nating  gas  and  the  oxygen  of  the  air  unite  chemically  witl 
rapidity. 

76.  Kindling  Point.  —  All  are  familiar  with  the  fact  tha 
wood  must  be  heated  before  it  will  take  fire.  There  is  { 
fixed  temperature  below  which  it  will  not  start  to  burn 
The  lowest  temperature  at  which  a  substance  will  burn  ii 
air  is  called  its  kindling  temperature.  The  kindling  pom 
of  any  one  substance  is  constant.  Materials,  however 
vary  greatly  in  their  kindling  temperature.  This  fact  ii 
made  use  of  in  an  ingenious  way  in  the  construction  of  i 

match.     The  ordinary  par 

^CHIEFLY  OXIDIZING  MATERIAL  «/       -L 

—CHIEFLY  LOW  KINDUNG  MATEH.AL  gjgj-g        Qf        ft        g^ 

FIG.    22.    --   CROSS    SECTION    OF    A      woo^    one    en(}    of 


has  been   soaked    in   par 

affin  and  then  dipped  in  a  mixture  of  glue,  phosphorus 
and  some  material  which  will  readily  give  off  oxy- 
gen. When  the  match  is  scratched,  the  friction  causes 
sufficient  heat  to  ignite  the  head  of  the  match  ;  this  ir 
burning  raises  the  temperature  of  the  paraffin  to  it; 
kindling  point,  and  the  burning  paraffin  raises  the  tern 
perature  of  the  wood  to  its  kindling  temperature. 

77.  A  Fuel  is  a  material  that  is  burned  for  the  purpost 
of  obtaining  heat.  Both  heat  and  light  are  produced  wher 
a  fuel  burns,  but  sometimes  heat  and  at  other  times  lighi 
is  the  form  of  energy  desired.  All  common  fuels,  such  as 
wood,  coal,  kerosene,  gasoline,  and  gas,  contain  carbon  anc 
hydrogen.  The  carbon  may  be  largely  uncombined,  as  ir 
hard  coal,  or  in  chemical  combination  with  hydrogen,  a* 
in  the  cases  of  kerosene,  gasoline,  and  gas,  or  united  witl 
hydrogen  and  oxygen,  as  in  the  case  of  wood.  Com 


PRODUCTS   OF   COMBUSTION 


93 


pounds  consisting  of  carbon  and  hydrogen  only  are  called 
hydrocarbons.  Acetylene  and  marsh  gas  are  such  com- 
pounds. Illuminating  gas  is  a  mixture  of  hydrogen,  car- 
bon monoxide,  and  various  hydrocarbons. 

78.  Products  of  Combustion.  —  Two  compounds  of  carbon 
and  oxygen  are  known,  carbon  monoxide,  CO,  and  carbon 
dioxide,  CO2.  During  the  complete  combustion  of  the 


Courtesy  of  The  Scientific  American. 

FIG.  23. —BURNING  OIL  WELL. 


94 


BURNING   AND  OXIDATION 


fuels  mentioned,  only  two  products  result ;  namely,  steam 
and  carbon  dioxide.  As  both  of  these  compounds  are  color- 
less gases,  they  pass  into  the  air  unobserved.  If  smoke  is 
formed  during  burning,  it  shows  that  the  combustion  is  not 
complete,  inasmuch  as  a  part  of  the  carbon  has  not  been 
burned  (Fig.  23).  The  ashes  left  in  the  stove  when  wood 
or  coal  is  burned  are  due  to  the  sand,  clay,  and  various 
other  kinds  of  mineral  matter  which  were  either  contained 
in  the  fuel  or  mixed  with  it. 

79.    Conditions  Necessary  for  Burning  to  Continue. — In 

order  to  have  burning  continue  after  being  started,  sub- 


FIG.  24. —  EXTINGUISHING  FLAMES  ON  CLOTHING. 

stances   that  will  enter  into   chemical   combination  with 
each  other  (fuel  and  oxygen)  must  be  supplied,  the  tern- 


CONDITIONS  NECESSARY  FOR  BURNING 


95 


perature  must  be  kept  above  the  kindling  point,  and  the 
products  of  combustion  must  be  carried  away.  The  re- 
moval of  any  one  of  these  conditions  will  cause  the  fire  to 
go  out,  and  the  methods  employed  for  putting  out  fires 
depend  upon  this  fact. 

In  the  case  of  a  burning  building,  water  is  the  agency 
usually  employed  (Fig.  21).  The  water  absorbs  heat  and 
lowers  the  temperature  of  the  burning  material  below  its 
kindling  point.  At  the 
same  time,  the  water 
and  the  steam  pro- 
duced from  it  lessen 
the  amount  of  air  in 
contact  with  the  burn- 
ing substance.  In  the 

11 


case  of  a  great  confla- 
gration, where  the  fire 
has  spread  over  such 
an  extended  area  that 
it  is  impossible  to  ex- 
tinguish it  by  water, 
the  combustible  mate- 
rial is  removed  by  dy- 
namiting buildings.  Other  illustrations  of  the  removal 
of  the  combustible  substance  are  the  back-firing  of  a 
forest,  the  plowing  around  a  field  of  burning  grass, 
and  the  carrying  away  of  highly  inflammable  substances 
from  the  vicinity  of  the  fire. 

The  means  most  commonly  employed  to  put  out  a  small 
fire  is  to  prevent  the  supporter  of  combustion  from  coming 
in  contact  with  the  burning  material.  A  rug  or  similar 
article  is  thrown  around  a  person  whose  clothing  has 
caught  fire  (Fig.  24).  Earth,  or  sand,  is  thrown  on  the 
burning  substance.  Fire  extinguishers,  which  replace  the 


FIG.  25.  —  FIRE  EXTINGUISHER. 


96  BURNING  AND   OXIDATION 

air  in  contact  with  the  burning  material  with  a  gas  that 
does  not  support  combustion,  are  used.  The  fire  extin- 
guisher shown  in  Fig.  25  is  used  to  throw  a  stream  of 
water  charged  with  carbon  dioxide  on  to  the  fire.  When 
the  extinguisher  is  inverted,  the  stopper  falls  out  of  the 
bottle,  allowing  the  sulphuric  acid  to  come  in  contact  with 
the  solution  of  sodium  bicarbonate  contained  in  the  body 
of  the  extinguisher.  Carbon  dioxide  is  produced  accord- 
ing to  the  equation  : 


H2SC>4    +  2NaHCO3  —  ^2CO2  +  2H2O    +  Na2SO4 

sulphuric  sodium  carbon  water  sodium 

acid  bicarbonate  dioxide  sulphate 

The  pressure  of  the  carbon  dioxide  generated  forces  the 
solution  out  through  the  hose.  "  Pyrene  "  extinguishers 
contain  carbon  tetrachloride,  a  highly  volatile  liquid,  whose 
vapor  does  not  burn. 

80.  Change  of  Energy  during  Burning.  —  Every  chemical 
action  is  accompanied  by  a  change  of  energy,  heat  being 
the  form  of  energy  most  frequently  taken  into  considera- 
tion.    In  some  instances,  heat  is  absorbed  during  a  chemi- 
cal change,  so  that  the  compound  formed  contains  more 
energy   than    its   constituents  did.       When  acetylene  is 
formed  from  the  elements  carbon  and  hydrogen,  a  large 
amount  of  energy  is  absorbed  ;  consequently,  when  acety- 
lene is  burned,  more  heat  is  liberated  than  would  be  pro- 
duced by  burning  equivalent  weights  of  uncombined  carbon 
and  hydrogen.     More  frequently,  however,  heat  is  liber- 
ated during  a  chemical  change.      When  this  is  of  sufficient 
intensity  to  produce  light,  burning  is  said  to  take  place. 
Burning  is  chemical  action  accompanied  by  light  and  heat. 

81.  Slow  Oxidation.  —  Everybody  is  familiar   with   the 
fact  that  iron  rusts  when  exposed  to  air.     Thin  layers  of 
linseed  oil  left  in  contact  with  air  are  converted  into  a 


SLOW  OXIDATION  97 

leathery  substance,  the  "  skin  "  which  forms  on  the  sur- 
face of  a  linseed  oil  paint  when  left  standing  in  an  open 
can.  Carbon  in  the  tissues  of  the  body  is  converted  into 
carbon  dioxide.  In  all  of  these  cases,  oxidation  has  taken 
place,  but  the  process  has  gone  on  so  slowly  that  no  light 
has  been  produced,  and  the  temperature  has  remained  low. 
These  examples  illustrate  the  process  of  slow  oxidation. 

In  certain  cases,  we  do  not  want  oxidation  to  take  place  ; 
for  example,  we  do  not  want  iron  to  rust,  so  we  prevent 
the  oxygen  of  the  air  from  coming  in  contact  with  the 
iron  by  covering  it  with  some  substance  such  as  paint, 
stove  polish,  zinc,  tin,  or  nickel.  In  other  cases  oxidation 
is  desirable.  Paints  contain  some  oil  which  will  oxidize 
to  produce  a  leathery  substance  capable  of  holding  the 
color  to  the  surface  of  the  material  painted.  Oils  which 
absorb  oxygen  and  are  converted  by  the  process  into  solids, 
are  called  drying  oils.  Linseed  oil,  fish  oil,  and  China 
wood  oil  are  the  principal  ones  used  in  paints.  Since  lin- 
seed oil  absorbs  oxygen  so  slowly  that  during  the  drying 
there  would  be  time  for  particles  of  dust  to  settle  on  the 
wet  paint,  some  substance,  called  a  drier,  is  added  to  the 
paint  to  hasten  the  process. 

If  the  heat  formed  during  slow  oxidation  is  not  carried, 
away  by  the  air  as  rapidly  as  it  is  produced,  the  body  be- 
ing oxidized  will  grow  warmer  and  its  kindling  tempera- 
ture may  finally  be  reached.  Spontaneous  combustion  is 
generally  brought  about  in  this  way. 

During  the  formation  of  carbon  dioxide  in  the  body,  the 
oxygen  taken  up  by  the  blood  in  the  lungs  slowly  unites 
with  the  carbon  compounds  in  the  body.  The  heat  of  the 
body  is  due  to  this  reaction.  If  the  oxidation  takes  place 
too  rapidly,  fever  results  ;  if  too  slowly,  a  temperature  be- 
low normal  is  produced.  In  the  latter  case,  doctors  often 
administer  oxygen  to  increase  the  rapidity  of  the  oxidation. 


98  BURNING  AND   OXIDATION 

The  same  amount  of  heat  is  generated  whenever  a  gram 
of  carbon  is  converted  into  carbon  dioxide.  If  the  time 
consumed  in  the  oxidation  is  long,  the  temperature  may 
remain  low  and  no  light  will  result.  The  process  is  then 
called  slow  oxidation.  If  the  time  consumed  is  short,  the 
kindling  temperature  will  be  reached  and  the  process  will 
then  be  one  of  combustion. 

SUMMARY 

Burning  is  chemical  action  accompanied  by  noticeable  light 
and  heat.  When  a  substance  burns  in  air  the  same  compound 
is  formed  as  when  that  substance  is  burned  in  oxygen.  This 
may  be  readily  illustrated  by  burning  an  element  whose  product  of 
combustion  can  be  easily  recognized.  When  oxygen  is  removed 
from  the  air,  burning  stops. 

The  gas  in  which  a  substance  burns  is  commonly  called  the 
Supporter  of  Combustion,  and  the  substance  burned  is  said  to  be 
the  Combustible. 

The  Kindling  Point  of  a  substance  is  the  lowest  temperature  at 
which  that  substance  will  burn  in  air.  The  kindling  temperature 
varies  greatly  with  the  kind  of  matter. 

A  Fuel  is  combustible  rriatter  used  to  produce  heat.  Carbon 
and  hydrogen  are  the  principal  elements  of  value  in  all  common 
fuels,  and  carbon  dioxide  and  steam  are  the  products  of  the  com- 
bustion desired.  Ashes  and  smoke  are  undesirable. 

Conditions  Necessary  for  Burning  are  a  temperature  at  least  as 
high  as  the  kindling  point  of  the  combustible  substance  and  a  supply 
of  fuel  in  contact  with  the  supporter  of  combustion.  A  removal 
of  either  of  these  conditions  will  cause  the  fire  to  go  out. 

A  compound  may  contain  more  energy  than  do  the  elements 
of  which  it  is  composed  when  they  are  in  a  free  condition. 

Slow  Oxidation  is  the  chemical  combination  of  a  substance  with 
oxygen  at  so  slow  a  rate  that  noticeable  light  is  not  produced. 


EXERCISES  99 

When  the  heat  produced  by  slow  oxidation  accumulates,  Spon- 
taneous Combustion  frequently  occurs.  Familiar  illustrations  of 
slow  oxidation  are  the  rusting  of  iron,  the  hardening  of  surface 
layers  of  linseed  oil  on  exposure  to  air,  and  the  production  of  car-' 
bon  dioxide  in  the  body. 

EXERCISES 

1.  Define  burning. 

2.  Does  burning  ever  take  place  in  the  absence  of  oxygen  ? 
Give  evidence  to  prove  your  answer. 

3.  Mention  cases  to  illustrate  the  fact  that  during  ordinary 
burning,  oxides  are  formed. 

4.  Why  is  oxygen  called  a  supporter  of  combustion,  while 
nitrogen  is  said  riot  to  support  combustion  ? 

5.  Is  oxygen  the  only  element  that  will  support  combus- 
tion ?     Explain. 

6.  Define  kindling  point,  kindling  temperature,  or  ignition 
point. 

7.  Show  how  the  structure  of  a  match  illustrates  the  fact 
that  all  substances  have  not  the  same  kindling  point. 

8.  Is  paper  used  in  starting  a  fire  because  it  has  a  lower 
kindling  temperature  than  wood  ?     Give  reasons  for  believing 
your  answer  to  be  correct. 

9.  From  a  chemical  standpoint,  what  is  smoke  ? 

10.  Why  is  it  more  difficult  to  burn  soft  coal  than  hard  coal 
without  producing  smoke  ? 

11.  Give  a  practical  illustration  of  putting  out  a  fire  by  (a) 
lowering  the  temperature  of  the  burning  material  below  its 
kindling  point ;   (5)  the  removal  of  the  combustible  substance  ; 
(c)  preventing  the  supporter  of  combustion  from  coming  in  con- 
tact with  the  combustible  material. 

12.  Name  a  compound  of  carbon  and  hydrogen  which  when 
burned  yields  more  heat  than  could  be  obtained  by  burning  the 
same  weight  of  carbon  and  hydrogen  in  a  free  condition. 


100  BURNING-  AND   OXIDATION 

13.  Define  slow  oxidation.     Why  should  not  the  terra  com- 
bustion be  used  in  connection  with  slow  oxidation  ? 

14.  Why  is  iron  often  coated  with  tin,  zinc,  or  nickel  ? 

15.  Why  are  substances  often  added  to  paint  to  increase  the 
rapidity  with  which  the  linseed  oil  takes  oxygen  from  the  air  ? 

f  16.    State  the  conditions  necessary  for  spontaneous  combus- 
tion. 

17.  Why  does  a  person  require  more  food  in  winter  than  in 
summer  ? 

18.  Why  is   pure  oxygen  often   administered  to  a  person 
having  pneumonia,  a  disease  by  which  the  effective  lung  area 
is  decreased? 

19.  What  happens  when  oxidation  takes  place  in  the  body 
with  more  than  normal  rapidity  ? 

20.  How  would  the  amount  of  heat  obtained  by  burning  a 
gram  of  carbon  in  oxygen  compare  with  that  liberated  when  a 
gram  of  carbon  is  converted  into  carbon  dioxide  in  the  body  ? 
How    would   the  temperatures   in   the   two   cases   compare  ? 
Explain. 


CHAPTER    XI 
FUELS 

82.  Definition    of    Fuels.  —  Fuels   are    substances   that 
unite  readily  with  the  oxygen  of  the  air,  giving  off  a  con- 
siderable amount  of  heat  in  the  process,  and  are  cheap 
enough  to  be  used  in  large  quantities  for  practical  pur- 
poses.    The  characteristics  desirable  in  them  are : 

(a)  high  calorific  power;  that  is,  the  property  of  fur- 
nishing a  large  amount  of  heat  per  unit  of  weight ; 
(£)  low  per  cent  of  ash ; 

(c)  freedom  from  objectionable  products  of  combustion ; 

(d)  low  cost  of  production  ; 

(e)  ease  of  transportation  and  handling. 

SOLID  FUELS 

83.  Wood  has  been  used  as  a  fuel  from  earliest  times. 
It  has  most  of  the  desirable  characteristics,  but  since  it  is 
no  longer  a  cheap  article  in  many  localities,  it  is  not  so 
much  used  as  formerly.     Wood  consists  chiefly  of   the 
chemical    compound    cellulose,     (C6H10O6)n.      When    it 
burns,  carbon  dioxide  and  water  are  formed. 

C6H1008     +    602— s-   6C02     +     5H30 

cellulose  oxygen  carbon  water 

dioxide 

The  ash  that  is  left  when  wood  or  other  fuel  burns  is  a 
residue  of  incombustible  mineral  matter.  Water  is  al- 
ways present  in  wood.  In  freshly  cut  wood  there  may  be 
as  high  as  50  %,  and  even  after  thorough  drying  by  long 

101 


102  FUELS 

standing,  as  much  as  20  %  may  remain.  The  presence  of 
water  in  any  fuel  lessens  the  heat  value.  The  best  woods 
for  heating  purposes  are  the  hard  varieties,  such  as  maple 
and  oak,  which  do  not  burn  rapidly. 

84.  Flames.  —  The  flame  that  is  seen  during  the  com- 
bustion of  most  fuels  consists  of  burning  gases,  which  have 
been  driven  out  by  the  heat  of  the  combustion.     Particles 
of  carbon  are  frequently  liberated  by  the  decomposition 
of  these  gases  during  the  process  of  burning,  and,  being 
heated  white  hot,  they  make  the  flame  luminous.     The 
presence  of  carbon  particles  is  readily  proved  by  the  fact 
that  a  cold  object  placed  in  contact  with  the  flame  be- 
comes covered  with  soot.     A  flame  that  does  not  carry 
particles  of  free  carbon,  as,  for  example,  the  flame  of  burn- 
ing hydrogen,  or  that  of  a  Bunsen  burner,  is  not  luminous. 

85.  Coal.  —  This  is  by  far  the  most  important  of  all 
fuels.     Most  of  the  commercial  enterprises  of  the  world 
depend  on  its  use.     We  mine  this  indispensable  article 
from  deposits  which  were  stored  up  millions  of  years  ago 
at  a  time  when  peculiar  conditions  existed  on  the  earth's 
surface.     A    dense    vegetation    flourished   in    swamplike 
land.     On  falling,  it  became  buried  under  mud  and  water, 
so  that  oxygen  did  not  have  access  to  it.     Thus  decay  in 
the  usual  manner  could  not  occur.     If  it  had,  the  carbon 
would  have  been  returned  to  the  air  in  the  form  of  carbon 
dioxide,  but,  under  the  conditions  that  existed,  the  carbon 
remained  and  was  transformed  into  coal.     According  to 
the  extent  of  the  transformation,  we  find  different  varieties. 
The  two  chief  kinds  are  bituminous  or  soft  coal,   and 
anthracite  or  hard  coal. 

86.  Bituminous  Coal.  —  This  variety  of  coal  has  under- 
gone less  decomposition  than  anthracite.     The  cellulose 


BITUMINOUS   COAL 


103 


of  which  it  was  originally  composed  has  been  so  changed 
that  from  50%  to  75%  of  the  weight  is  uncombined  car- 
bon. From  15%  to  40%  of  the  remainder  is  composed 


10 


BITUMINOUS  ANTHRACITE 

COAL  COAL 


30     - 


1000 


FIG.  26. — COMPOSITION  AND  HEAT  VALUE  OF  COMMON  FUELS. 

of  compounds  known  as  hydrocarbons.  These  are  dis- 
tilled from  the  coal  as  it  burns,  and  give  a  smoky,  lumi- 
nous flame.  The  "  softer  "  the  coal,  the  more  smoky  the 
flame.  For  most  purposes  this  is  an  undesirable  charac- 


104  FUELS 

teristic.  Cities  in  which  soft  coal  is  used  are  notorious 
as  "  dirty  "  cities.  Furnaces  in  which  such  fuel  is  used 
should  be  arranged  to  consume  the  sooty  matter. 

Soft  coal  has  many  advantages.  It  has  high  heat 
value,  is  easily  kindled,  and  burns  very  quickly.  It  is 
the  chief  fuel  used  in  industrial  operations. 

87.  Anthracite  Coal.  —  This    variety   is    found   only   in 
mountain    regions    where    nature    subjected    the   buried 
vegetable  matter  to  much  heat  and  pressure  during  the 
changes  that  took  place  in  the  process  of  mountain  forma- 
tion.    As  a  result  the  coal  lost  much  of  its  volatile  mat- 
ter.    It    contains    from    80  %    to    90  %    of    uncombined 
carbon,    and    from    5%    to    10%    hydrocarbons.     Conse- 
quently it  burns  with  almost  no  flame.     This  makes  it  a 
very  clean  fuel,  admirably  adapted  for  use  in  cities. 

88.  Ash  from  Coal.  —  Both  varieties  of  coal  leave  a  con- 
siderable amount  of  ash  on  burning.     The  per  cent  of  ash 
varies  greatly  in  different  varieties  of  coal,  and  in  differ- 
ent grades  of  the  same  variety.     It  is  the  most  important 
factor  in  determining   the  comparative  heating  value  of 
different  samples  of  coal.     The  true  ash  is  the  residue  of 
mineral  matter  which  was  absorbed  from  the  earth  by  the 
growing  plant.     In  addition,  there  is  apt  to  be  present  in 
coal  a  certain  amount  of  slate,  which  is  merely  the  hard- 
ened clay  that  became  imbedded  in  the  coal  during  the 
process  of  its  formation.     In  good  grades  of  coal  most  of 
the  slate  is  removed  when  it  is  prepared  for  the  market. 
In  lower  grades,  much  of  the  slate  remains,  and  in  such 
cases  there  may  be  as  high  as  30  %  to  35  %  of  ash  after 
the  coal  is  burned. 

89.  Fuels  related  to  Coal.  —  There  are  several  of  these  fuels 
not  much  used  in  this  country.     The  important  ones  are  : 


REFINING   OF  PETROLEUM  105 

Peat,  formed  from  moss  that  has  been  buried  under 
water ;  it  contains  much  ash  and  a  high  per  cent  of  water. 

Lignite,  a  form  of  coal  in  which  the  vegetable  matter 
has  been  so  little  changed  that  it  still  resembles  wood. 

Oannel  Coal,  a  form  of  soft  coal  very  rich  in  hydrocar- 
bons. It  burns  with  much  flame,  making  a  beautiful  fire 
for  open  grates. 

Briquettes,  a  manufactured  fuel  much  used  in  Europe, 
and  rapidly  coming  into  use  in  this  country.  The  pow- 
dered coal  that  is  formed  in  mining  and  preparing  the 
article  for  the  market,  and  which  would  otherwise  be  a 
waste  product,  is  mixed  with  tarry  matter  and  com- 
pressed into  molds. 

LIQUID  FUELS 

90.  Petroleum.  —  This  is  the   most  important  of   liquid 
fuels.     Like  coal,  it  is  a  deposit  that  was  formed  ages  ago 
within  the  earth.     Little  is  known  of  its  origin.     Within 
recent  years  petroleum  has  come  into  use  in  its  unrefined 
state  as  an  important  fuel  for  railroads,  steamships,  and 
factories.     It   competes   successfully  with    coal  in    those 
parts  of  the  country  where  it  occurs  and  where  coal  is 
scarce.     This  is  particularly  true  in  Texas  and  California. 
It  has  a  high  heat  value,  and  the  important  property  of 
leaving  no  ash.     In  addition,  since  it  is  a  liquid,  it  can  be 
transported  in  pipe  lines,  often  for  hundreds  of  miles. 
This  is  a  very  important  economic  consideration. 

91.  Refining  of  Petroleum.  —  Petroleum   as   it   is   found 
within  the  earth  consists  of  a  mixture  of  many  hydrocar- 
bons.    By  a  process  of  distillation  these  are  very  easily 
separated,  and  various  products  are  obtained.     The  crude 
oil  is  heated,    and  gases   that  pass  off  are   again  turned 
into  liquids  by  condensation.     The  distillation  is  partly 


106  FUELS 

of  the  destructive  variety ;  that  is,  a  certain  amount  of 
chemical  decomposition  is  effected  in  the  original  petro- 
leum. By  this  means  the  nature  of  the  products  can  be 
varied  to  meet  commercial  needs.  The  products  range 
from  light,  low-boiling  oils,  like  gasoline,  to  the  heavy  oils 
that  are  used  for  lubricating  machinery. 


FIG.  27. —  OIL  FIELD. 

The  process  of  petroleum  refining  also  includes  treat- 
ment to  remove  impurities,  such  as  sulphur  compounds, 
which  would  form  undesirable  products  of  combustion. 
This  subject  is  more  fully  treated  in  Chapter  XXXII. 

92.  Gasoline.  —  This  article,  considered  an  undesirable 
product  in  the  early  history  of  petroleum  refining,  has  of 
recent  years  become  one  of  the  most  valuable,  owing  to 
the  increasing  use  of  gasoline  engines  in  automobiles, 
motor  boats,  and  for  many  other  purposes.  Gasoline  is 
formed  by  the  condensation  of  gases  that  pass  off  at  com- 
paratively low  temperatures  during  the  distillation  of 


ALCOHOL  107 

petroleum.  Its  valuable  characteristic  is  its  volatility ; 
that  is,  the  ease  with  which  it  becomes  a  gas.  This  same 
characteristic  is  also  the  cause  of  many  accidents  in  han- 
dling gasoline.  Its  vapor,  when  mixed  with  air,  is  highly 
explosive.  It  is  dangerous  only  under  these  conditions. 

Gasoline  is  a  mixture  of  hydrocarbons  whose  chemical 
composition  can  be  represented  by  the  general  formula 
Cre  H2n+2,  in  which  n  stands  for  the  number  of  carbon  atoms. 
Using  one  of  these  hydrocarbons,  hexane,  C6H14,  as  a  type, 
the  equation  for  the  burning  of  this  kind  of  fuel  is 

2  C6H14  +  19  O2  — *-  12  CO2  +  14  H2O 

hexane  oxygen  carbon  water 

dioxide 

93.  Kerosene.  — The  character  of  this  fuel  is  best  under- 
stood by  comparing  it  with  gasoline,  which  it  in  general 
resembles,  except  that  it  is  much  less  volatile.     It  is  ob- 
tained from  the  crude  petroleum  at  a  temperature  just 
above  that  at  which  gasoline  passes  off.     Its  chief  use  is 
as  an  illuminant  in  lamps.     It  is  also  increasingly  used  as 
a  fuel  in  cooking  stoves,  where  a  city  gas  system  is  not 
available,  and  for  the  operation  of  the  kerosene  engine. 

94.  Alcohol.  —  Although  at  present   used  as  a  fuel  on 
only  a  very  small  scale,  alcohol  is  nevertheless  of  impor- 
tance in  this  connection.     Its  heat  value  is  very  high,  and 
it  burns  with  a  clean  flame.     The  chemical  composition  is 
represented  by  the  formula  -C2H5OH ;  the  equation  for 
the  burning  is 

C2H5OH  +   302  — -^2C02  +  3H20 

alcohol  oxygen  carbon  water 

dioxide 

Alcohol  is  adapted  for  use  in  cooking  or  heating  on  a 
small  scale,  especially  where  transportation  is  a  difficult 


108  FUELS 

matter,  as  in  Arctic  exploration  or  mountain  climbing.  It 
has  been  used  successfully  as  a  fuel  for  gas  engines,  and 
it  may  ultimately  be  the  chief  fuel  for  this  purpose,  since 
the  supply  of  petroleum  within  the  earth  is  limited.  Al- 
cohol is  made  by  the  fermentation  of  vegetable  matter 
and  can  be  produced  indefinitely  in  any  quantity. 

GASEOUS  FUELS 

95.  Coal  Gas.  —  The  gas  obtained  by  heating  soft  coal 
until  it  decomposes  chemically,  came  originally  into  use 
solely  as  an  illuminant.  But,  as  the  process  of  manufacture 
improved,  and  as  uses  were  found  for  the  by-products,  the 
cost  of  producing  the  gas  was  so  reduced  that  it  has  now 
come  into  use  as  a  fuel.  In  large  cities  it  is  the  most 
important  fuel  for  cooking  purposes.  It  has  numerous 
points  of  superiority  for  this  use.  It  can  be  distributed 
through  pipes  at  low  cost,  it  burns  with  a  clean  flame, 
the  heat  can  be  concentrated  in  one  spot,  and  no  handling 
of  fuel  or  ashes  is  necessary. 

The  process  of  destructive  distillation  by  which  coal  gas 
is  obtained  consists  in  heating  bituminous  coal  in  retorts 
without  access  of  air.  A  variety  of  products  is  obtained, 
including  the  by-products  named  below.  The  gas  is  col- 
lected in  gas  tanks  after  undergoing  a  certain  amount  of 
purification.  It  consists  of  a  mixture  of  gases  in  approxi- 
mately the  per  cents  named.  ^ 

Hydrogen        47 

Methane,  CH4 40.5 

Carbon  monoxide,  CO 6 

Ethane,  C2H6 4 

Carbon  dioxide,  nitrogen,  oxygen,  total  of      ...       2.5 

Other  hydrocarbons  of  high  illuminating  power  occur  in 
small  amounts. 


WATER    GAS  109 

An  important  by-product  of  the  coal  gas  process  is  coke, 
which  is  itself  a  very  important  fuel.  It  has  a  chemical 
composition  similar  to  that  of  hard  coal,  but  it  burns  more 
rapidly,  because  it  is  porous  in  structure.  It  can  be  used 
as  a  substitute  for  hard  coal.  It  is  used  on  a  large  scale  in 
producing  iron  from  iron  ore  (Chapter  XL).  H 

Coal  tar  and  ammonia  are  two  other  important  by- 
products of  coal  gas  manufacture.  Their  extraction  and 
uses  are  described  in  Chapter  XXXII. 

96.  Water  Gas.  — This  fuel  and  illuminant  is,  like  coal 
gas,  a  manufactured  product.  The  operation  makes  use 
of  the  fact  that  steam  reacts  with  incandescent  carbon  and 
forms  hydrogen  and  carbon  monoxide  : 

C     +    H2O — ^    CO     +      H2 

carbon  steam  carbon         hydrogen 

monoxide 

Either  hard  coal  or  coke  may  be  used  as  a  source  of  the 
carbon.  It  is  brought  to  a  state  of  incandescence  by 
blowing  a  blast  of  air  through  it  for  a  few  minutes. 
The  white-hot  fuel  is  then  exposed  to  the  action  of  steam, 
and  the  reaction  described  above  takes  place.  The  coke 
is  not  allowed  to  cool  below  1000°.  When  this  tempera- 
ture is  reached,  air  is  again  blown  in.  These  alternations 
occur  about  every  fifteen  or  twenty  minutes.  Both  of  the 
gaseous  products  are  combustible,  and  hence  the  process 
obviously  produces  a  cheap  fuel.  When  the  gas  is  to  be 
used  as  an  illuminant,  a  further  step  is  essential,  since  the 
mixture  of  carbon  monoxide  and  hydrogen  burns  with  a 
non-luminous  flame.  To  render  the  flame  luminous,  an 
admixture  of  hydrocarbons  is  necessary.  This  operation 
is  called  "  enriching "  the  gas.  It  consists  in  spraying 
in  gas  oil,  and  subjecting  the  mixture  to  a  high  tem- 
perature, so  that  the  liquid  hydrocarbons  are  converted 


110 


FUELS 


NATURAL 
GAS 


WATER       PRODUCER 
GAS  GAS 


permanently  into  gases.     When  the  water  gas  burns,  these 
are  decomposed  by  the  heat  of  the  flame,  and  particles  of 

carbon  exist  for  a  brief  in- 
stant in  the  free  state,  and 
become  heated  to  the  point 
at  which  they  emit  light. 

Water  gas  has  less  heat 
value  than  coal  gas  and  is 
more  dangerous  in  case  of 
leakage,  because  it  has  a 
higher  per  cent  of  carbon 
monoxide,  which  is  a  very 
poisonous  substance. 

97.  Producer  Gas.  —  Pro- 
ducer gas  is  used  as  a  fuel 
only,  chiefly  for  gas  engines 
(Chapter  XXXIV)  and  in 
metallurgical  and  other 
manufacturing  operations. 
It  is  made  at  a  low  cost  by 
blowing  air  through  incan- 
descent coke  or  coal.  It 
consists  of  carbon  monoxide 
mixed  with  much  nitrogen. 
Sometimes  steam  is  blown 
in  with  the  air  blast,  in  which 
case  the  product  contains 
some  hydrogen.  The  heat 

value    of    producer  gas  is  low,  but  this  is  offset  by  the 

low  cost  of  production. 

98.    Natural  Gas.  —  A   gas   of   low   illuminating   power 
and  high  heat  value  is  found  stored  in  some  parts  of  the 


28.  —  VOLUME     COMPOSITION 
OF  FUEL  GASES. 

X=  Minor  Constituents. 


ACETYLENE 


111 


earth.  It  is  contained  in  a  highly  compressed  state  in  the 
pores  of  rocks.  By  drilling  wells  to  these  strata  it  can  be 
made  available  as  a  fuel.  In  many  parts  of  the  country  it 
is  the  chief  fuel.  It  is  composed  mainly  of  the  hydro- 
carbon'methane,  CH4.  Natural  gas  is  always  found  asso- 
ciated with  petroleum  deposits. 

99.    Acetylene.  —  This  gas  is  used  chiefly  as  an  illumi- 
nant,  and  its  use  for  this  purpose  is  discussed  in  Chapter 
XIV.       It    has    an    important 
use    as    a    fuel    in    connection 
with   the  oxyacetylene  burner, 
a    means    of   obtaining   an    ex- 
tremely high  temperature.     The 
burner  is  so  arranged  that  the 
acetylene  is  mixed  with  oxygen 
at  the   moment  it   issues   from 
the  jet.     The  result  is  a  small 
flame  of  intense  heat,  so  hot  that 
it  will,  for  example,  melt  steel 
quickly.       This    gives    a    very     a 
quick  and  convenient  means  of    ,| 
cutting  steel  beams  and  plates 

(Chapter  XXXIII).  FIG.  29.-ACETVLENE  GENERATOR. 

Calcium  carbide  is  necessary 

in  the  production  of  acetylene  for  commercial  purposes. 
This  substance  is  made  by  heating  coke  with  quicklime 
in   the   electric   furnace,   which   develops    a    temperature 
•  sufficiently  high  for  the  following  reaction  to  occur : 


3C 

carbon 


CaO 

quicklime 


CaC2 

calcium 
carbide 


CO 

carbon 
monoxide 


When    calcium   carbide   comes  in  contact  with  water, 
acetylene  is  rapidly  formed : 


112  FUELS 

CaC2        +        2H20      — »-       C2H2          +        Ca(OH)2 

calcium  water  acetylene  slaked 

carbide  lime 

SUMMARY 

Fuels  are  Desirable  in  proportion  as  they  have  the  following 
properties  in  a  high  degree  :  (a)  high  heat  value,  (b)  low  per  cent 
of  ash,  (c)  freedom  from  undesirable  combustion  products, 
(d)  low  cost  of  production,  (e)  ease  of  transportation  and  handling. 

Important  Solid  Fuels  are  coal,  wood,  and  coke.  They  contain 
carbon  or  carbon  compounds  as  the  combustible.  Different 
varieties  of  coal  contain  from  50%  to  90%  of  free  carbon,  the 
remainder  being  hydrocarbons  and  ash.  Bituminous  coals  have 
a  high  per  cent  of  hydrocarbons,  varying  from  15%  to  40%. 
Wood  consists  mostly  of  cellulose,  (C6H1005)n. 

Important  Liquid  Fuels  are  kerosene,  gasoline,  crude  petroleum, 
and  alcohol.  The.  first  three  are  mixtures  of  hydrocarbons ; 
alcohol  is  the  hydroxide  of  a  hydrocarbon.  Liquid  fuels  have  the 
great  advantage  of  leaving  no  ash,  and  of  being  very  easy  to  trans- 
port and  handle. 

Important  Gaseous  Fuels  are  coal  gas,  water  gas,  producer  gas, 
and  natural  gas.  They  consist  of  hydrogen,  hydrocarbons,  and 
carbon  monoxide,  or  mixtures  of  these.  Their  convenience 
is  so  great  that  they  are  increasingly  used,  and  they  could  be 
employed  for  most  fuel  purposes  if  their  cost  were  not  compara- 
tively high. 

Flames  are  burning  gases.     Luminosity  in  flames  is  caused  by, 
the  presence  of  particles  of  free  carbon  that  are  heated  to  in- 
candescence.     Flames   in  which   free   carbon   is  not  produced 
during  the  act  of  combustion  are  non-luminous. 

Ash  is  the  residue  of  incombustible  mineral  matter  originally 
present  in  the  vegetable  matter  from  which  the  fuel  was  derived. 


EXERCISES  113 

• 
EXERCISES 

1.  Under  similar  conditions  of  air  supply,  which  fuel  would 
burn  most  slowly  :  wood,  soft  coal,  or  hard  coal  ?     Why  ? 

2.  Why  does  wood  snap  and  crackle  when  it  burns  ? 

3.  Why  does  maple  make  a  better  stove  wood  than  white 
pine  ? 

4.  Which  kind  of  coal  burns  with  much  flame  ?     Why  ? 

5.  Why  is  the  flame  from  cannel  coal  exceedingly  luminous  ? 

6.  Why  is  it  more   desirable  to  burn  waste  coal  dust  in 
the  form  of  briquettes  instead  of  as  the  original  powder  ? 

7.  How  could  you  determine  the  per  cent  of  hydrocarbons 
in  a  sample  of  coal  ?     The  per  cent  of  ash  ? 

8.  In  coal  mines  impressions  of  fern  leaves,  tree  trunks, 
etc.,  are  sometimes  found.     How  do  you  account  for  this  ? 

9.  What  defect  exists  if  densely  black,  sooty  smoke  issues 
from  a  factory  chimney  ?     How  could  the  trouble  be  remedied  ? 

10.  Why  would  it  be  dangerous  to  use  gasoline  in  lamps  ? 

11.  Which  fuel,  kerosene  or  gasoline,  is  most  used  in  gas 
engines  ?     Why  ? 

12.  Why  do  we  not  use  crude  petroleum  in  lamps  ? 

13.  What  are  the  chief  differences  in  the  composition  of 
coal  gas  and  water  gas  ?     Of  producer  gas  and  water  gas  ? 

14.  What  reasons  can  you  assign  for  the  growing  popularity 
of  gaseous  fuels  for  cooking  purposes  ? 

15.  Acetylene  gives  an  exceedingly  luminous  flame.  Explain. 

16.  WThy  do  coals  differ  in  their  per  cent  of  ash  ? 

17.  Define  a  fuel ;  a  flame. 

18.  Name  compounds  that  are  formed  in  the  combustion  of 
wood  ;  of  coal ;  of  kerosene  ;  of  illuminating  gas. 

19.  Compare  kerosene  and  alcohol  as  fuels. 

20.  When  alcohol  is  burned  what  becomes  of  the  oxygen 
that  it  contains  ? 


CHAPTER   XII 


FIREPLACES  AND  STOVES 

100.  The  Fireplace  is  a  primitive  arrangement  for  the 
indoor  use  of  fire.  A  fireplace  (Fig.  30)  is  a  cavity  walled 
with  fireproof  material,  usually  either  brick  or  stone,  built 
into  one  side  of  the  room,  and  opening 
into  a  chimney.  Wood  is  the  form  of 
fuel  generally  used.  In  order  to  in- 
crease the  surface  of  the  fuel  in  contact 
with  the  air,  the  wood  is  placed  upon 
andirons,  which  hold  it  above  the  coals 
and  ashes.  An  apron,  or  blower,  which 
is  a  sheet  of  metal  supported  on  legs, 
may  be  put  in  front  of  the  fire.  When 
the  blower  is  placed  properly,  there 
is  a  strong  draft  under  and  upward 
between  the  sticks  of  wood,  so  that  the 
gaseous  products  of  combustion,  to- 
gether with  the  unconsumed  portions 
of  the  air,  are  carried  rapidly  out  of 
the  chimney.  Under  these  conditions, 
the  fire,  once  started,  burns  brightly,  but  nearly  all  of 
the  heat  passes  up  the  chimney.  When  the  blower  is 
removed,  less  air  passes  between  the  sticks  of  wood  and 
the  draft  is  diminished  so  that  the  fuel  burns  less  rapidly, 
while  more  of  the  heat  enters  the  room.  The  draft  may 
be  still  further  decreased  by  partly  closing  the  chimney  by 
a  damper. 

114 


FIG.  30.  —  SECTION  OF 
A  FIREPLACE. 


STOVES  115 

There  is  no  device  for  obtaining  artificial  heat  that  is 
so  cheerful  as  the  open  fireplace,  and  there  is  none  that  is 
more  wasteful.  From  80  %  to  90  %  of  the  heat  from  the 
burning  fuel  is  usually  permitted  to  pass  up  the  chimney 
without  increasing  the  warmth  of  the  room.  Recently 
devices  have  been  invented  for  using  the  hot  gases  as  they 
pass  up  the  chimney  to  warm  a  .secondary  current  of  air 
which  enters  the  room.  In  this  way  the  efficiency  of  the 
fireplace  has  been  greatly  increased. 

If  it  were  not  for  the  pleasure  to  be  derived  from  sit- 
ting by  an  open  fire,  watching  the  glowing  coals  and  the 
fantastic  shapes  taken  by  the  flames,  the  open  fireplace 
would  long  since  have  passed  out  of  use  in  most  localities. 
The  gas  log  and  asbestos  grate  are  poor  substitutes  for  the 
open  fireplace.  When  gas  is  used  as  fuel,  the  products  of 
combustion  are  frequently  allowed  to  mingle  with  the  air 
of  the  room.  While  this  lessens  the  waste  of  heat,  it 
greatly  diminishes  the  purity  of  the  air. 

101.  Stoves.  —  A  stove  is  a  nearly  closed  receptacle,  gen- 
erally made  of  iron,  in  which  fuel  is  burned  for  obtaining 
heat.  When  coal  or  wood  is  used  as  fuel,  a  system  of 
drafts  arid  dampers  regulates  the  supply  of  air  that  enters 
the  stove.  The  principles  involved  may  be  illustrated  by 
a  description  of  the  ordinary  coal  stove  used  for  heating 
purposes.  In  the  front  of  the  stove,  at  a  lower  level  than 
the  grate  on  which  the  coal  is  placed,  is  a  row  of  openings, 
the  draft,  with  a  slide  for  closing  them.  A  similar  row  of 
openings,  also  provided  with  a  slide,  placed  at  a  higher 
level  than  the  fuel,  constitutes  the  check.  In  the  stove- 
pipe is  a  sheet  of  iron,  the  damper,  arranged  so  that  it 
either  slides  or  may  be  turned  to  any  degree  between  a 
vertical  and  a  horizontal  position. 

To  start  a  fire  in  the  stove,  crumpled  pieces  of  paper  or 


116  FIREPLACES  AND   STOVES 

shavings  are  placed  on  the  grate  and  small  pieces  of  wood 
are  laid  loosely  upon  them.  The  check  is  closed  and  the 
draft  and  damper  are  opened.  The  pieces  of  paper,  or  the 
shavings,  are  then  lighted.  Only  a  small  quantity  of  heat 
is  required  to  raise  the  temperature  of  the  edge  of  a  piece 
of  paper  to  its  kindling  point,  and  the  burning  paper  soon 
sets  the  wood  on  fire.  Air  is  drawn  through  the  draft 
and  passes  between  the  pieces  of  wood,  causing  them  to 
burn  rapidly.  At  the  same  time,  the  products  of  combus- 
.tion  in  gaseous  form  are  carried  away  through  the  chim- 
ney. As  soon  as  the  wood  is  burning  briskly,  a  small 
amount  of  coal  is  placed  on  the  fire.  When  this  first  por- 
tion of  coal  has  become  thoroughly  ignited,  more  coal  is 
added  to  fill  the  fire  box.  Coal  should  never  be  placed 
above  the  lining  of  the  fire  box  as  the  lids  of  the  stove  are 
damaged  by  overheating. 

The  temperature  of  the  stove  is  regulated  by  manipu- 
lating the  draft,  damper,  and  check.  When  the  draft  is 
closed,  only  a  small  quantity  of  air  enters  the  stove.  This 
quantity  may  be  still  further  diminished  by  closing  the 
damper  in  the  pipe.  If  the  check  is  opened,  the  draft 
closed,  and  the  damper  nearly  shut,  cool  air  passes  over 
instead  of  between  the  pieces  of  coal.  Under  these  con- 
ditions only  a  small  portion  of  the  air  which  enters  the 
stove  is  heated  to  the  kindling  point  of  the  coal,  and  com- 
bustion takes  place  very  slowly. 

When  the  draft  and  damper  are  both  open,  the  oxygen 
of  the  air,  entering  the  bottom  of  the  fire  box  and  earning 
in  contact  with  the  lower  layer  of  hot  coal,  first  unites  with 
the  carbon  to  form  carbon  dioxide  : 


C    +   02  —  ^  C02 

carbon      oxygen  carbon 

dioxide 


WOOD   STOVES  117 

If  the  carbon  dioxide  thus  formed  does  not  pass  too 
rapidly  through  the  upper  layers  of  hot  coal,  it  combines 
with  more  carbon  so  that  carbon  monoxide  is  formed : 

CO2   +   C  — >-  2  CO 

carbon      carbon          carbon 
dioxide  monoxide 

Carbon  monoxide  is  a  very  poisonous  gas  and  should  never 
be  allowed  to  escape  into  the  room.  The  blue  flame  fre- 
quently seen  on  top  of  the  coal  is  burning  carbon  mon- 
oxide. When  the  check  is  open,  the  carbon  monoxide  is 
likely  to  be  burned  to  carbon  dioxide: 

2  CO   +   02— - ^2C02 

carbon         oxygen  carbon 

monoxide  dioxide 

The  damper  should  never  be  closed  so  tightly  that  the 
gaseous  products  of  combustion  will  not  escape  into  the 
chimney.  A  sleeping  room  should  never  contain  a  coal 
fire  in  a  stove  with  the  damper  entirely  closed,  because 
carbon  monoxide  is  likely  to  be  formed  and  to  escape 
into  the  room  while  the  occupants  are  asleep.  Many 
persons  have  lost  their  lives  by  breathing  air  poisoned  by 
carbon  monoxide  from  a  stove  near  their  beds.  Although 
pure  carbon  monoxide  is  odorless,  other  gases  having  odors 
are  formed  during  the  burning  of  coal  so  that,  if  a  person 
is  awake,  the  escape  of  gas  into  the  room  will  be  noticed. 
Ashes  should  not  be  allowed  to  accumulate  in  a  coal  stove, 
as  they  prevent  air  from  entering  the  draft.  They  should 
be  shaken  into  the  pan  below  the  grate  and  removed 
daily. 

102.  Wood  Stoves.  —  A  wood  stove  differs  from  a  coal 
stove  chiefly  in  the  form  of  the  grate  ;  in  fact,  wood  stoves 
frequently  have  no  grate,  the  draft  being  placed  just  above 
the  space  intended  for  ashes. 


118 


FIREPLACES  AND   STOVES 


FIG.    31.  —  KITCHEN    RANGE  —  SMOKE    DAMPER 
CLOSED. 


103.  The  Kitchen 
Range.  —  Cook 
stoves,  in  addition 
to  the  draft,  damper, 
and  check,  have  a 
smoke  damper. 
When  the  smoke 
damper  is  closed 
(Fig.  31),  the  hot, 
gaseous  products  of 
combustion  pass 
around  the  oven 
before  entering  the 
chimney,  and  the 
oven  becomes  heated.  If  the  smoke  damper  is  open  (Fig. 
32),  there  is  direct  communication,  over  the  oven,  between 
the  fire  box  and  chimney,  so  that  only  the  top  of  the 
oven  is  warmed. 
Dust,  carried 
with  the  gaseous 
products  of  com- 
bustion, is  de- 
posited on  top 
and  under  the 
even.  This  de- 
posit is  a  poor 
conductor  of  heat 
and  obstructs  the 
passage  of  the 

gases  under  the 

FIG.  32.  —  KITCHEN  RANGE  —  SMOKE  DAMPER  OPEN. 
oven.      It    must 

be  removed  occasionally  or  the  oven  will  not  be  heated  as 
it  should.  Often  the  top  of  the  oven  is  so  constructed 
that  all  of  the  ashes  cannot  be  easily  removed. 


FURNA CES 


119 


Hot  air 


104.  Furnaces.  —  A  furnace  is  an  arrangement  for  heat- 
ing a  house  indirectly.  Three  classes  of  furnaces  are  in 
common  use  :  the  hot-air  furnace  (Fig.  33),  the  hot- 
water  furnace,  and  the 
steam  furnace ,  Consider- 
ing these*  in  the  order 
named,  the  combustion 
of  the  fuel  is  used  to 
heat  air,  to  warm  water, 
or  to  convert  water  into 
steam.  The  heated  air  is 
conveyed  through  large 
pipes  to  the  various  rooms 
to  be  warmed.  The  steam 
or  hot  water  passes 
through  pipes  to  radiators 
set  in  the  rooms  to  be 
heated.  In  the  radiators, 
the  steam  or  hot  water  is 
cooled,  and  then  returns 
through  pipes  to  the  fur- 
nace, the  heat  meanwhile 
entering  the  rooms.  One 
fire  thus  provides  heat  for 

the  whole  house,  and  the  fuel  and  ashes  are  kept  out  of 
the  living  rooms. 

SUMMARY 

An  Open  Fireplace  is  a  walled  space  built  into  one  side  of  a 
room,  in  which  fuel  may  be  burned.  Andirons  are  used  to  keep 
the  fuel  above  the  ashes,  and  an  apron  or  blower  is  used  to  in- 
crease the  draft  between  the  pieces  of  fuel.  The  open  fireplace 
is  the  most  cheerful  arrangement  for  warming  a  room,  but  is 
most  inefficient. 


FIG.  33.  —  HOT-AIR  FURNACE. 


120  FIREPLACES  AND   STOVES 

Gas  Logs  and  Asbestos  Grates  are  substitutes  for  open  fire- 
places. The  products  of  combustion  are  often  permitted  to  mix 
with  the.  air  of  the  room,  which  is  thus  made  impure. 

A  Stove  is  a  nearly  closed  receptacle  in  which  fuel  is  burned. 
A  heating  stove  is  generally  provided  with  a  draft,  a  check,  and 
a  damper.  The  Draft  permits  air  to  enter  the  stove  beneath  the 
grate.  The  Check  permits  air  to  enter  above  the  grate.  The 
Damper  regulates  the  size  of  the  opening  through  which  products 
of  combustion  escape  to  the  chimney. 

The  Kitchen  Range  has,  in  addition  to  the  draft,  the  check, 
and  the  damper,  a  Smoke  Damper  which  can  be  used  at  will  to 
guide  the  products  of  combustion  directly  into  the  chimney,  or 
cause  them  first  to  pass  around  the  oven.  The  space  under  the 
oven  should  be  kept  nearly  free  from  ashes,  but  a  thin  layer  of 
ashes  should  be  allowed  to  accumulate  on  top  of  the  oven  to  pre- 
vent overheating. 

The  Furnace  is  a  form  of  stove,  generally  placed  in  the  cellar, 
used  to  heat  air  or  water,  by  means  of  which  the  heat,  of  the 
burning  fuel  is  indirectly  carried  to  the  living  rooms.  Modern 
furnaces  are  economical  and  tend  to  keep  the  living  rooms  clean. 

Paper  or  shavings  are  used  to  start  a  fire  because  a  very  small 
quantity  of  heat  is  required  to  bring  the  temperature  of  this  thin 
material  to  its  kindling  point,  and  because  they  present  a  large 
surface  to  the  air.  Burning  wood  'is  used  to  raise  the  temper- 
ature of  the  coal  to  its  kindling  point. 

The  principal  products  of  combustion  when  hard  coal  is  used  as 
fuel  are  carbon  dioxide  and  carbon  monoxide.  Carbon  monoxide 
should  be  burned  to  carbon  dioxide.  Carbon  monoxide  is  a 
deadly  poison  and  should  never  be  permitted  to  enter  a  living 
room. 

EXERCISES 

1.  What  is  the  chief  advantage  of  an  open  fireplace  ?  The 
principal  disadvantage  ? 


EXERCISES  121 

2.  Make  a  drawing  of  a  coal  stove  used  for  heating.    Show 
the  location  of  the  grate,  the  draft,  the  check,  and  the  damper. 

3.  Should  (1)  the  damper,  (2)  the  check,  and  (3)  the  draft 
be  opened  or  closed  (a)  when  the  fire  is  started  ?    (6)  In  order 
to  have  the  fire  keep  as  long  as'  possible  ? 

4.  Does  opening  the  check  cause  the  fire  to  burn  more  or 
less  rapidly  ?     Explain. 

5.  Why  is  the  use  of  the  check  a  wasteful  method  of  regu- 
lating the  rapidity  of  burning  ? 

6.  Give  directions  for  starting  a  coal  fire. 

7.  Why  may  either  paper  or  shavings  be  used  in  starting 
a  fire  ? 

8.  .  What  two  oxides  of  carbon  are  formed  during  the  burn- 
ing of  coal  in  a  stove  ? 

9.  Why  should  not  carbon  monoxide  be  permitted  to  mix 
with  the  air  of  a  living  room  ? 

10.  How  does  a  kitchen  range  differ  from  a  heating  stove  ? 

11.  Tell  how  the  (a)  check,  (5)  draft,  (c)  smoke  damper,  and 
(d)  damper  should  be  manipulated  for  a  "  quick  oven*"      For  a 
"slow  oven." 

12.  What  most  frequently  causes  a  stove  to  bake  poorly 
after  it  has  been  in  use  for  some  time  ? 

13.  How  can  an  oven  be  prevented  from  baking  "too  hard 
on  top  "  ? 

14.  What  is  the  chief  disadvantage  in  using  a  stove  to  heat 
a  room  ? 

15.  What  are  some  of  the  advantages  in  the  use  of  a  hot- 
water  system  for  heating  ?  A  disadvantage  ?  * 

16.  What  is  the  chief  advantage  of  a  steam-heating  plant  ? 
The  principal  disadvantage  ?  * 

17.  What  great  advantage  has  a  hot-air  system  over  a  hot- 
water  or  a  steam-heating  system  ?  * 

*  Exercises  15,  16,  and  17  are  for  class  discussion. 


CHAPTER  XIII 


GAS  AND  GASOLINE   STOVES 

105.  The  Bunsen  Burner.  —  Before  considering  the  gas 
range  it  may  be  well  to  make  a  study  of  the  burner  uni- 
versally used  in  chemical  laboratories  as  a  source  of  heat. 
Its  chief  advantage  is  that  it  gives  a  hot,  smokeless  flame. 
This  burner  bears  the  name  of  the  distinguished  German 
chemist  who  invented  it,  Robert  Wilhelm  Bunsen.  Tha 
bunsen  burner  (Fig.  34)  consists  of 
three  parts:'  the  base,  the  barrel,  and 
the  ring.  The  base  is  provided  with 
a  horizontal  tube  (for  attaching  a 
rubber  hose  to  connect  the  burner 
with  a  gas  cock)  and  a  small,  central 
gas  way  or  "  spud,"  through  which  the 
gas  passes  to  the  barrel.  The  barrel 
is  a  metal  tube,  with  two  or  more 
holes  near  the  lower  end,  made  to  screw 
on  the  base.  The  ring  fits  the  lower 
end  of  the  barrel,  and  has  holes  which  may  be  either 
brought  over  those  in  the  barrel,  or  over  its  solid  portion. 
When  the  burner  is  in  use,  gas  enters  the  barrel  through 
the  spud,  mixes  with  a  supply  of  air  only  partially  sufficient 
for  complete  combustion,  and  the  mixture  rises  to  the  top 
of  the  barrel,  where  it  is  ignited  and  burns  in  the  surround- 
ing air.  The  air  entering  the  holes  at  the  base  of  the 
barrel  is  termed  "  primary  air,"  and  is  secured  by  the  gas 
issuing  at  a  high  speed  from  the  spud.  This  stream  of 

122 


FIG.  34. — SECTION  OF 
BUNSEN  BURNER. 


THE  BUN  SEN  FLAME  123 

gas  produces  a  partial  vacuum  in  the  barrel,  causing  air 
to  enter  the  holes  near  its  base,  and  to  mix  with  the  gas 
before  leaving  the  burner.  The  supply  of  gas  and  air 
should  be  adjusted  so  that  a  non-luminous  flame  of  suit- 
able size  is  obtained,  and  so  that  the  flame  will  not  "  strike 
back."  The  supply  of  gas  entering  the  barrel  is  regulated 
by  varying  the  size  of  the  opening  in  the*  spud,  and 
the  supply  of  air  which  mixes  with  the  gas  is  regulated  by 
turning  the  ring  so  as  to  vary  the  size  of  the  holes  through 
which  the  air  enters  the  barrel.  If  the  gas  pressure  is 
low,  the  mixture  of  gas  and  air  may  burn  downward  more 
rapidly  than  it  issues  from  the  barrel.  In  this  case,  the 
burner  will  strike  back;  that  is,  the  flame  will  pass  down 
the  barrel  to  the  end  of  the  spud,  at  which  point  incom- 
plete combustion  will  take  place.  This  not  only  produces 
a  disagreeable  odor,  but  is  likely  to  heat  the 
base  of  the  burner  sufficiently  hot  to  melt 
the  rubber  hose,  and  the  escaping  gas  may 
be  set  on  fire. 

In  the  inner  portion  of  the  bunsen  flame,  the 
gas  is  only  partly  burned,  and,  on  this  account, 
it  is  able  to  take  oxygen  from  metallic  oxides 
placed  in  it;  that  is,  to  reduce  them.  It  is, 
therefore,  called  the  reducing  flame.  The  ex- 
treme tip  of  the  outer  flame  causes  many  sub- 
stances to  oxidize  when  they  are  heated  in  it, 
and  is  consequently  called  the  oxidizing  flame. 
The  portion  of  the  flame  having  the  highest  temperature 
is  just  above  the  inner  cone  (Fig.  35). 

106.  The  Gas  Range.  —  The  burners  of  a  gas  range  are 
modified  bunsen  burners.  Two  types  of  burners  are  used: 
one  intended  for  use  in  boiling  or  frying,  and  the  other 
for  use  during  baking  or  broiling.  Burners  for  use  dur- 


124 


GAS   AND    GASOLINE   STOVES 


FIG.  36.  —  RING  BURNER. 


ing  boiling  are  de- 
signed to  produce 
a  number  of  flames 
arranged  in  a  ring 
or  star,  so  as  to 
heat  large  surfaces 
(Figs.  36  and  37). 
A  section  of  a 

burner  connected  to  a  gas  cock  is  shown  in  Fig.  38.     The 

"  primary  air"  is  secured  by  the  velocity  of  the  gas  from 

the  "spud"  at  A.     This 

stream  of  gas  produces 

a  partial  vacuum  in  the 

air  chamber  B,  causing 

air  to  rush  in  through 

the  mixer  disk  jP,  and 

mix  with  the  gas  in  the 

throat    a.       The    mix-  FIG.  37. -STAR  BURNER. 

ture  passes  to  the  ports 

(7,  where  ignition  takes  place.     The  amount  of  air  that 

mixes  with  the  gas  previous  to  ignition  is  regulated  by 


FIG.  38.  —  RING  BURNER  SECTION. 


the  adjustable  mixer  disk  (Fig.  39).  The  heat  from 
the  flame  causes  the  surrounding  air  to  expand  and 
rise.  A  supply  of  "secondary  air"  is  thus  continually 


EFFICIENCY  OF   GAS-RANGE  BURNERS        125 

drawn  up  to  the  flame  of  the  burner.  If  too  much  "  sec- 
ondary air "  is  allowed  to  reach  the  flame  jets,  the  ef- 
ficiency of  the  burner  is  lowered,  as  a  quantity  of  air  is 
heated  which  serves  no  useful  purpose.  In  the  improved 
burner  (Fig.  36),  this  is  taken  care  of  by  making  the 
openings  D,  D  of  such  a  size  that  they 
will  supply  sufficient  secondary  air  to  insure* 
complete  combustion,  and  at  the  same  time 
prevent  loss  of  efficiency  by  avoiding  the 

heating    of   an   unnecessary   quantity    of  air. 

FIG.  39» 

The  flow  of  gas  being  constant,  the  air  is  reg- 
ulated by  the  adjustable  mixer  disk  (Fig.  89)  which  is 
held  in  place  at  .E  (Fig.  38)  by  a  set  screw. 

107.  Efficiency  of  Gas  Range  Burners.  —  The  most  effi- 
cient flame  of  a  gas-range  burner  is  one  in  which  the 
cross-sectional  area  of  the  inner  cone  is  larger  than  that  of 
the  outer  cone,  and  is  of  a  blue  color.  If  an  insufficient 
supply  of  primary  air  is  admitted  through  the  mixer  disk, 
yellow  tips  will  be  seen  on  the  inner  cone.  If  too  much 
air  is  admitted,  the  burner  will  either  flash  back  and  burn 
at  the  spud,  or  the  inner  cone  will  be  small  and  of  a  light 
green  color.  In  a  well-designed  burner,  the  adjustment 
of  the  mixer  disk  permits  the  most  efficient  flame  to  be 
obtained  under  varying  conditions  of  service. 

The  distance  between  the  top  of  the  burner  and  the 
bottom  of  the  cooking  vessel  should  be  such  that  only  the 
extreme  tips  of  the  outer  cone  of  the  flames  touch  the 
vessel.  This  distance  for  a  gas  range  should  never  be  less 
than  1^  inches.  If  the  distance  be  less,  the  flame  is  chilled 
by  contact  with  the  vessel  and  arrested  combustion  results. 
This  condition  may  be  readily  detected  by  the  garlic-like 
odor  that  is  given  off.  s 

In  boiling  articles  of  food  over  a  gas  flame,  it  is  well  to 


126  GAS  AND   GASOLINE   STOVES 

remember  that  after 
water  commences  to 
boil,  its  temperature 
remains  practically 
constant,  no  matter 
how  much  heat  is 
applied.  No  increase 
of  temperature  is  ob- 
tained by  causing  the 
water  to  evaporate 
(boil  away)  rapidly. 
The  burners  of  a 
gas  range  should 
never  be  blackened, 
as  the  ports  are  likely 
to  become  clogged. 
The  burners  should 
be  removed  occasion- 
ally and  cleaned  by 
boiling  them  in  a 

solution  of  washing  soda.  Care  must  be  taken  to  replace 
them  in  their  proper  positions,  as  each  burner  requires  a 
gas  way  of  a  definite  size. 

108.  Gas  Range  Oven  and  Broiler.  —  The  oven  and  broiler 
are  heated  by  several  burners  constructed  on  the  same 
principle  as  those  used  in  boiling  and  frying,  but  are  of 
a  different  shape  (Fig.  41). 

The  broiler  and  oven  are  lined  for  a  threefold  purpose  : 

1st.  To  provide  a  dead  air  space  of  ^  inch  around  the 
sides  and  back  of  the  range.  This  prevents  excessive  loss 
of  heat  from  the  oven  by  radiation. 

2d.  To  provide  flues  to  supply  the  secondary  air  to  the 
oven  burners,  and  to  supply  heated  air  to  the  oven  in  such 


FLUE   OF  GAS  RANGE 


127 


a  way  that  the  heat  is  so  distributed  that  the  oven  will 
bake  evenly. 

3d.  To  provide  supports  for  the  oven  and  broiler 
racks. 

The  oven  door  should  always  be  open  when  the  burners 
under  the  oven  are  lighted.  When  the  gas  is  first  turned 
on,  some  of  it  frequently  enters  the  oven  and  .forms  a  mix- 
ture with  the  air  which  may  explode  violently  on  being 
ignited.  In  heating  the  oven  for  baking,  the  cocks  should 
be  turned  on  full  so  as  to  permit  the  baking  temperature 


FIG.  41.  —  IMPROVED  OVEN  BURNER. 
A,  throat;  B,  baffle;  C,  flame  jets. 

to  be  quickly  reached.  After  reaching  this  point,  the 
cocks  should  be  partly  closed,  as  only  a  small  amount  of 
gas  is  necessary  to  maintain  a  constant  temperature  after 
the  oven  has  once  become  hot.  The  bottom  is  the  hottest 
part  of  the  oven,  and,  in  order  to  bake  evenly,  an  article 
should  be  supported  so  that  it  will  not  rest  on  the  bottom 
of  the  oven.  During  broiling,  the  broiler  door  should  be 
left  partly  open  to  prevent  the  meat  from  scorching. 

109.  Flue  of  Gas  Range.  —  A  gas  stove  is  generally  pro- 
vided with  a  flue  collar  which  may  be  connected  with  the 
chimney  by  a  pipe,  in  order  to  dispose  of  the  products  of 
combustion  and  the  heat  discharged  when  the  oven  is 


128 


GAS  AND   GASOLINE   STOVES 


in  use.  This  naturally  would  tend  to  keep  the  kitchen 
cool.  When  the  gas  stove  is  connected  with  a  chimney, 
a  properly  designed  draft  diverter  should  be  provided,  so 
that  if  there  should  be  a  back  draft,  the  combustion  of  the 
gas  burners  will  not  be  affected. 

110.    Gasoline  Stoves.  --The  gasoline  stove  (Fig.  42)  is 
similar  in  construction  to  the  gas  range,  but  is  provided 

with  a  different  kind  of 
burner.  The  gasoline  is 
stored  in  a  tank,  placed  on 
one  side  of  the  stove  and 
at  a  higher  level  than  the 
burners.  In  the  older  types 
of  gasoline  stoves  a  little 
gasoline  is  run  into  a  cup 
under  the  burner,  and 
ignited.  The  burning  gaso- 
line heats  the  burner.  When 
the  burner  is  sufficiently 
hot,  a  valve,  connecting  the 
burner  with  the  pipe  lead- 
ing from  the  tank,  is  opened.  The  gasoline,  while  passing 
through  the  hot  burner,  is  converted  into  gas,  which 
burns  with  a  flame  similar  to  that  of  the  gas  range. 

A  more  recent  form  of  burner  is  shown  in  Fig.  43.  A 
torch  (A),  saturated  with  gasoline,  is  lighted  and  slid  into 
its  casing.  This  causes  hot  air  to  rise  through  the  pipe 
(jo).  This  hot  air  warms  the  perforated  evaporating  tube 
(a).  Gasoline  is  permitted  to  drop  through  the  sight 
feed  (/)  upon  the  heated  evaporating  tube,  where  it  turns 
into  a  heavy  vapor.  This  mixture  of  gasoline  vapor  and 
air  passes  to  the  burner,  where  it  is  lighted.  A  small 
flame  at  the  base  (e)  of  the  burner  causes  a  continuous 


FIG.  42.  —  GASOLINE  STOVE. 


SUMMARY 


129 


place 


circulation   through  the  pipes  after   the  burner    is  once 
lighted. 

Nearly  all  of  the  many  accidents  that  have  taken 
during  the  use  of  gasoline  stoves 
have  been  caused  by  filling  the 
gasoline  tank  while  the  burner 
was  lighted.  The  person  in 
charge  did  not  realize  that 
gasoline  is  a  very  volatile 
liquid,  and  that  a  mixture  of 
gasoline  vapor  and  air  may  be 
highly  explosive.  Most  of  the 
modern  gasoline  stoves  are  made 
so  that  it  is  impossible  to  fill 
the  tank  while  the  burner  is  FIG.  43. —  GASOLINE 
lighted.  RATION  BURNER. 


EVAPO- 


SUMMARY 

The  Essential  Parts  of  a  Bunsen  Burner  are  the  base,  the  barrel, 
and  the  ring. 

Mixture  of  Gas  and  Air.  —  Gas  is  mixed  with  air  before  com- 
bustion takes  place.  The  quantity  of  gas  and  of  air  should  be  so 
regulated  that  a  clean  flame  of  desirable  size  is  produced,  and 
striking  back  does  not  occur. 

The  inner  portion  of  the  bunsen  flame  is  a  Reducing  Flame,  and 
the  extreme  tip  is  an  Oxidizing  Flame. 

The  Burners  of  a  Gas  Range  are  modified  bunsen  burners.  The 
burner  under  the  oven  should  not  be  lighted  when  the  oven  door 
is  closed. 

The  Gasoline  Stove  is  a  modified  gas  stove.  Gasoline  is  vapor- 
ized, and  a  mixture  of  the  vapor  with  air  is  burned.  The  tank  of 
a  gasoline  stove  should  never  be  filled  while  the  burner  is  lighted. 


130  GAS  AND   GASOLINE  STOVES 

EXERCISES 

1.  Name  the  essential  parts  of  a  bunseii  burner. 

2.  How  is  (a)  the  amount  of  gas  entering  the  barrel  regu- 
lated?    (6)  The  amount  of  air? 

3.  How  does  the  amount  of  heat  produced  by  burning  a 
cubic  foot  of  gas  in  a  burner  producing  a  colorless  flame  com- 
pare with  that  produced  by  a  burner  consuming  the  same 
amount  of  gas,  but  producing  a  yellow  flame  ? 

4.  How  do  the  two  flames  mentioned  in  3  compare  in  size? 
Which  produces  the  more   intense  heat  per  square  inch  of 
flame? 

5.  What  are  the  advantages  to  be  gained  by  the  use  of  a 
bunsen  burner? 

6.  Which  portion  of   the  bunsen  flame  has  the  highest 
temperature  ?     Which  is  an  oxidizing  flame  ?     Which  is  a  re- 
ducing flame  ? 

7.  What  causes  a  bunsen  burner  (a)  to  strike  back;  (b)  to 
produce  a  smoky  flame  ? 

8.  How  may  the   striking   back  of  a  bunsen  burner  be 
prevented  ? 

9.  Explain  how  a  fire  may  be  started  by  a  bunsen  burner 
that  has  struck  back. 

10.  Show  that  the  burners  of  a  gas  stove  are  modified  bun- 
sen  burners. 

11.  Why  should  the  burners  of  a  gas  stove  be  kept  clean  ? 

12.  Why  is  the  oven  of  a  gas  stove  likely  to  "  bake  too  hard 
on  the  bottom  "  ?     How  can  this  be  prevented  ? 

13.  Why  should  the  oven  door  of  a  gas  range  be  open  when 
the  burners  are  lighted  ? 

14.  How  does  a  gasoline  stove  resemble  a  gas  stove  ? 


EXERCISES  131 

15.  Why  should  the  tank  of  a  gasoline  stove  never  be  filled 
when  a  burner  is  lighted  ? 

16.  Why  is  it  dangerous  lo  have  gasoline  fed  to  the  burners 
of  a  stove  more  rapidly  than  it  is  vaporized  ? 

17.  Why  should  gasoline  be  kept  in  a  cool  place  in  a  tightly 

closed  vessel  ? 

• 

18.  Under  what  conditions  will  gasoline  vapor  explode  ? 

19.  Give  at  least  two  reasons  why  it  is  essential  that  gas 
cocks  be  kept  in  such  a  condition  that  they  can  be  tightly 
closed. 

20.  In  boiling   articles  of   food  on  a  gas  stove,  why  is  it 
wasteful  after  boiling  commences  to  burn  more  than  enough 
gas  to  keep  the  water  at  the  boiling  temperature  ? 


CHAPTER   XIV 


OIL  AND  GAS  LIGHTS 

111.  The  Candle  is  the  simplest  arrangement  for  artificial 
lighting.  A  candle  consists  of  solid  fat  or  wax  molded 
around  a  braided  wick  of  cotton  thread.  When  the  wick 
is  lighted,  the  material  of  which  the  candle  is  composed 
melts,  forming  a  small  cup  filled  with  liquid  fat.  The 
liquefied  fat  is  drawn  up  the  wick  by  capillarity,  and  heat 
converts  it  into  vapor  which  burns  with  a  flame. 

Aflame  is  simply  a  vapor  or  gas  in  the  process  of  burn- 
ing. A  burning  solid 
glows,  but  does  not 
produce  a  flame.  This 
may  be  illustrated  by 
burning  a  piece  of 
charcoal  from  which 
all  of  the  volatile 
matter  has  been  re- 
moved. The  charcoal 
glows  brightly,  but  no 
flame  is  formed. 

112.  The  Kerosene 
Lamp  is  next  to  the 
candle  in  simplicity 

FIG.  44. —  KEROSENE  LAMP.  ,,  ,.  rr»u 

of  construction.      Ihe 

oil    is    drawn    from   the    reservoir   of   the    lamp    by  the 
capillarity  of  the  wick,  and  its  vapor  burns  with  a  flame. 

132 


KEROSENE  LAMP 


133 


Kerosene  is  a  mixture  of  hydrocarbons.  The  hydrogen 
burns  more  readily  than  the  carbon,  so  that  the  carbon 
would  be  liberated 
in  the  form  of  soot, 
if  it  were  not  for 
the  special  con- 
struction of  the 
lamp  burner  and 
the  use  of  a  chim- 
ney to  insure  a 
proper  supply  of 
oxygen.  The 
burner  is  made  so 
that  air  is  mixed 
with  the  kerosene 
vapor  just  before 
it  takes  fire  (Fig. 
44).  In  the  "Ro- 
chester "  burner,  a 

large  flame  is  con- 

0  FIG.  45.  —  ROCHESTER  BURNER. 

fined    in    a    small 

space  by  making  the  wick  cylindrical.  Air  is  drawn 
through  the  lamp  to  the  inside  of  the  flame,  in  addition  to 
the  air  supplied  to  the  outside  of  the  flame  (Fig.  45). 

113.  The  Flashing  Point  of  an  oil  is  the  temperature  at 
which  a  mixture  of  oil  vapor  aiid  air  will  take  fire  and 
burn  momentarily,  or  "flash."     Most  states  require  that 
the  flash  point  of  kerosene  shall  not   be  below  110°  F. 
(44°  C.). 

114.  Explosive    Mixtures.  —  A   little    gasoline    may   be 
burned  in  an  open   dish  with  safety,  but  a  mixture  of 
gasoline  vapor  and  air  may  burn  so  rapidly  that  afi^xplo- 


134 


OIL   AND   GAS  LIGHTS 


sion  will  result.  Since  such  substances  as  gasoline,  ben- 
zine, and  naphtha  evaporate  rapidly  when  exposed  to  air, 
they  should  never  be  used  near  an  open  flame,  as  the 
explosive  mixture  of  their  vapor  and  air  is  likely  to  be 
ignited.  A  kerosene  of  low  flashing  point  is  dangerous 
to  use  in  lamps,  since  an  explosive  mixture  of  its  vapor 
and  air  might  be  formed  in  the  lamp.  In  the  case  of  any 
gas  which  is  used  for  lighting  or  heating,  there  is  a  range 
of  mixtures  of  the  gas  and  air  which  will  burn  explo- 
sively. Any  mixture  of  air  and  hydrogen,  in  which  the 
hydrogen  forms  from  10%  to  66%  of  the  whole,  will  ex- 
plode when  ignited,  the  most  violent  explosion  taking 
place  when  29%  of  the  mixture  is  hydrogen. 

;The  explosive  limits  of  the  mixture  of  acetylene 
with  air  are  wider  than  the  combination  of  other 
combustible  gases  in  common  use.     A  mixture 
of  air  and  acetylene,  containing  from  3  %  to  30  % 
of  acetylene,  will  burn  explosively. 
115.    Gasoline  Lights.  —  There  are  many  de- 
vices for  burning  gasoline  for  lighting  purposes. 
FlG     46    Their  object   is  to  convert   the   gasoline   into 
—GASOLINE   vapor  either  by  means  of  heat  (Fig.  46)  or  by 
TORCH.          forcing  air  through  it. 

116.  Gas  Burners. — Two  classes 
of  gas  burners  are  in  common 
use,  the  fishtail  burner  (Fig. 
47),  and  burners  for  use  with 
mantles.  The  fishtail  burner  is 
a  device  which  causes  the  gas  to 
spread  out  in  a  thin  sheet  as  it  is- 
sues from  the  burner,  so  that  suffi- 
cient air  to  burn  all  of  the  carbon 
is  brought  in  contact  with  the  gas. 


FIG.  47.  —  FISHTAIL  FLAME. 


GAS  BURNERS 


135 


In  the  case  of  burners  with  mantles,  before  the  gas  is 
burned  it  is  mixed  with  sufficient  air  to  make  a  mixture 
that  will  yield  a  colorless  flame.  Two  forms  of  lamps  for 
use  with  mantles  are  in  common  use:  the  upright  lamp 
and  the  inverted  lamp.  The  detailed  construction  of 
both  upright  and  inverted  lamps  comprises  the  following 
essential  features: 

1.  Bunsen  tube. 

2.  Bunsen  base. 

-  3.    Gas-adjustment  means. 

4.  Air-adjustment  means. 

5.  Mixing  chamber. 

6.  Supports  for    mantle,    chimneys,    glassware    or   re- 
flectors. 

Practically  the  only  structural  difference  between  the 
upright  and  inverted  form  of  lamps  is  the  burning  of  the  gas 


Mixing 
chamber 


Gallery 


Bunsen  base 


as  adjustment 
ir  adjustment 


hermostat 

Crown  for 
olding  glass- 
ware 


lefractory 
burner  tip 


FIG.  48. — UPRIGHT  MANTLE  BURNER.    FIG.  49.  —  INVERTED  MANTLE  BURNER. 


136  OIL  AND   GAS  LIGHTS 

and  the  placing  of  the  mantle  in  an  upright  position  in  the 
upright  burner,  and  the  burning  of  the  gas  and  the  placing 
of  the  mantle  in  a  downward  or  inverted  position  in  the  in- 
verted burner.  The  difference  in  lighting  efficiency  and 
distribution  of  light,  however,  is  marked,  the  upright 
burner,  distributing,  with  reflectors,  only  45  %  of  its  total 
light  below  the  horizontal,  while  the  inverted  burner, 
without  a  reflector,  distributes  67  %  of  the  total  light  below 
the  horizontal  —  the  place  where  the  light  is  most  needed. 
In  addition  to  this  one  fact,  the  inverted  burner  has  the 
following  advantages : 

1.  Improved  efficiency  and  economy. 

2.  Superior  decorative  possibilities. 

3.  Greater  durability  and   longer  candle  power  life  of 
the  mantle. 

4.  Units  naturally  adapting  themselves  to  all  conditions 
and  uses. 

Figures  48  and  49  show  respectively  the  cross  sections  of  a 
modern  upright  and  a  modern  inverted  gas  burner.  Both 
of  these  types  of  lamps  may  be  secured  in  various  sizes, 
ranging  in  gas  consumption  from  1.5  cubic  feet  per  hour 
to  4.5  cubic  feet  per  hour  for  the  upright,  and  from  1.5  cubic 
feet  per  hour  to  9.0  cubic  feet  per  hour  for  the  inverted. 
Groupings  of  a  number  of  upright  or  inverted  mantles  in 
one  inclosing  globe  are  made,  this  unit  being  known  as 
the  "gas  arc." 

117.  Gas  mantles  are  composed  of  mixtures  of  oxides  of 
certain  rare  elements,  chiefly  thorium  and  cerium.  The 
better  grades  of  mantles  are  made  by  dipping  thread  made 
from  China  grass  into  a  solution  containing  thorium  and 
cerium  nitrates,  and  then  weaving  the  impregnated  thread 
and  making  from  the  woven  material  a  mantle  of  the  re- 


ACETYLENE  137 

quired  shape.  Heat  converts  the  thorium  and  cerium 
nitrates  into  oxides.  A  finished  mantle  contains  99  %  of 
thorium  oxide  and  1  %  of  cerium  oxide.  The  heat  of  the 
burning  gases  causes  the  mantle  to  glow  brightly. 

118.  Gas  Lighters. —  With  the  advent  of  the  incandes- 
cent mantle  burner  came  the  development  of  the  pilot  ig- 
nition system.      This  consists  of  a  by-pass    around  the 
main  gas  valve,  allowing  a  small  stream  of  gas  to  pass 
through  a  tube  of  small  interior  diameter,'  terminating  in 
a  small  flame  tip  located  close  to  the  mantle.     The  tip  or 
pilot  remains  lighted  when  the  main  gas  valve  is  closed. 
When  this  valve  is   opened  so   as   to  admit   gas  to   the 
burner,   the  pilot  ignites   the  gas   and  lights  the  lamp. 
These  pilots  consume  a  very  small  amount  of  gas,  and  af- 
ford a  quick  and  convenient  means  of  lighting  the  lamp. 

In  another  scheme,  a  device  on  the  incandescent  mantle 
itself  replaces  the  pilot  light  as  a  means  of  ignition.  It 
consists  of  a  small  ball  or  pellet  of  platinum  sponge 
(platinum  black  or  very  finely  divided  metallic  platinum) 
which  becomes  heated  to  incandescence  by  the  action  of 
the  hydrogen,  oxygen,  and  carbon  monoxide  in  the  gaseous 
mixture,  and  causes  the  ignition  of  this  mixture,  thus 
lighting  the  lamp.  The  life  of  these  pellets  is  very  short 
since  each  ignition  causes  them  to  partially  solidify. 

119.  Acetylene  is  frequently  used  as  an  illuminating  gas, 
especially  for  automobile  lamps.     It  is  generated  either  by 
slowly  dropping  water  on  calcium  carbide  or  by  dropping 
granulated  calcium  carbide  into  water. 

As  acetylene  is  very  rich  in  carbon,  a  special  form  of 
burner  (Fig.  50)  is  required  to  prevent  the  formation  of 
soot.  Not  only  is  the  range  of  explosive  mixtures  of  acet- 
ylene and  air  greater  than  that  of  other  illuminating 


138 


OIL  AND   GAS  LIGHTS 


GAS  GAS        gases,  but  the  violence 

AIR 

of  the  explosion  is  far 
greater  than  in  the 
case  of  mixtures  of 
other  illuminating 
gases  with  air.  The 
tremendous  violence  of 
such  explosions  is  due 
not  only  to  the  great 
volume  of  the  gaseous 
products,  but  also  to 
the  fact  that  the 

ACETYLENE  BURNER.  chemical  energy  latent 

in  the  acetylene  molecule  is  suddenly  liberated.  It  is 
important  to  keep  this  fact  in  mind  when  dealing  with 
acetylene,  and  never  use  a  free 
flame  to  examine  acetylene  ap- 
paratus. The  flame  (Fig.  51) 
produced  by  the  acetylene 
burner  leaves  little  to  be  de- 
sired so  far  as  the  quality  of 
the  light  is  concerned. 


FIG.  50. 


120.  Prest-0-Lite,  so  exten- 
sively used  in  automobile 
lamps,  is  acetylene  dissolved 
in  acetone.  The  Prest-O-Lite 
tank  (Fig.  52)  is  filled  with 
asbestos  which  has  been  soaked 
in  acetone.  On  forcing  acet- 
ylene into  such  a  tank,  it  dis- 
solves in  the  acetone.  When  FIG.  51.— ACETYLENE  FLAME. 
the  valve  of  the  tank  is  opened,  the  pressure  on  the 
inside  is  reduced,  and  the  acetylene  passes  out  of  solution 


BLAUGAS 


139 


and,  by  being  made  to  pass  through  a  pressure  reducing 
valve,  may  be  delivered  at  the  lamp  at  any  desired  pressure. 

121.  Blaugas.  —  Petroleum  is  a  more  or  less  pure  mix- 
ture of  hydrocarbons.  During  the  distillation  of  petro- 
leum (Chapter  XXXII),  the  distillate  is 
separated  into  many  portions  and  therefore 
the  process  is  called  fractional  distillation. 
The  better-known  liquids  obtained  by  the 
fractional  distillation  of  petroleum  are 
gasoline,  naphtha,  benzine,  and  kerosene. 
Gas  oil  is  one  of  the  substances  obtained 
during  the  fractional  distillation  of  petro- 
leum, after  the  lighter  oils  just  mentioned 
have  been  distilled  off.  When  gas  oil  is 
heated  to  a  high  temperature  in  an  appa- 
ratus free  from  air,  it  decomposes.  Oil  gas 
is  one  of  the  products  of  decomposition. 

Herman  Blau,  in  1901,  perfected  a  process 
for  liquefying  oil  gas,  transporting  the 
liquid,  and  reconverting  it  into  gas  de- 
livered at  a  pressure  suitable  for  use  in 
lighting  and  heating.  Briefly  stated,  the 
process  is  as  follows :  The  portion-  of  the 
oil  gas  that  liquefies  at  ordinary  temper- 
atures under  a  pressure  of  about  20  atmos- 
pheres is  run  into  strong  steel  bottles,  until  the  liquid  fills 
about  three  fourths  of  each  bottle.  These  bottles  are  trans- 
ported to  places  where  the  gas  is  to  be  consumed.  Three 
bottles  constitute  a  set.  The  three  bottles  are  placed  in  a 
small  fireproof  room,  called  an  expander  box,  located  outside 
of  the  building  in  which  the  gas  is  to  be  used  (Fig.  53). 
Two  of  the  bottles  are  connected  with  a  pressure-reducing 
apparatus  at  the  same  time,  but  the  valve  of  only  one  of 


Courtesy  of  the 
Prest-O-Lite  Co. 

FIG.  52. 


140 


OIL   AND   GAS  LIGHTS 


them  is  opened.  The 
liquid,  drawn  from  the 
bottom  of  the  bottle, 
passes  to  a  valve  which 
reduces  the  pressure  so 
that  the  liquid  changes 
into  a  gas.  The  gas  is 
stored  in  a  tank  called 
an  expansion  tank.  On 
leaving  the  expansion 
tank,  the  gas  passes 
through  a  pressure  reg- 
ulator to  the  pipes  of 
the  house,  where  it  may 
be  used  in  the  same  way 
as  ordinary  illuminating 
gas.  When  the  con- 
tents of  one  bottle  have 
been  consumed,  the  valve 

is  closed,  the  valve  of  the  second  bottle  opened,  and  the 

empty  bottle   is   exchanged   for   the   third    bottle.     The 

empty  bottle  is  returned  to  the  factory, 

where  it  is  exchanged  for  a  full  bottle. 
Blaugas,    in    burning,    gives   a  bright 

light,  with  a  flame  of  high  temperature. 

It  has  a  low  explosion  range. 


FIG.    53.  —  BLAUGAS 


BOTTLES 
Box. 


AND    Ex- 


122.  Illumination.  —  The  following 
principles  may  be  of  value  in  determin- 
ing the  quality  of  light  which  should  be 
used  for  illumination  : 

The    intrinsic    brightness    (glare)    of 
light  within  the  field  of  vision  should  be  reduced,  so  that 
the  light  will  not  fatigue  or  strain  the  eye. 


FIG.  54.  —  RELA- 
TIVE VOLUME  OF 
GAS.  LIBERATED 
FROM  BLAUGAS 
BOTTLE. 


ILLUMINATION  141 

When  light  strikes  an  object,  part  of  the  rays  are  ab- 
sorbed by  the  object,  part  pass  through  it,  if  it  is  trans- 
parent or  translucent,  part  are  diffusely  reflected,  and  part 
regularly  reflected.  This  last  case  is  worthy  of  further 
consideration.  In  our  daily  life,  the  results  of  this  regular 
reflection  from  objects  in  the  direct  line  of  vision  are 
serious,  whether  the  reflection  comes  from  the  polished  or 
glass  tops  of  desks  or  tables,  from  the  polished  metal  of  a 
machine,  or  from  the  highly  glazed  surface  of  the  paper  in 
the  book  or  magazine  that  one  reads.  This  regularly  re- 
flected light  strains  and  fatigues  the  eye,  making  it  im- 
possible for  one  to  see  well.  To  obviate  this  serious  trouble, 
the  lighting  sources,  where  exposed  to  view,  should  be 
surrounded  by  good  diffusing  media  of  considerable  area 
and  of  low  intrinsic  brightness. 

Objects  are  visible  because  of  their  differences  in  color, 
and  in  intensity  or  brightness.  The  relative  differences 
in  intensity  are  largely  produced  by  shadows.  If  the 
light  in  a  room  were  perfectly  diffused,  there  would  be 
no  shadows  and  the  lighting  might  be  entirely  inadequate 
even  though  the  intensity  of  illumination  were  correct. 
In  order  to  produce  shadows  there  must  be  direct  light. 
Enough  diffused  light,  however,  must  also  be  present 
to  enable  one  to  see  in  the  shadows,  but  not  so  much 
that  the  shadows  will  lose  their  sharpness  and  so  lose  their 
power  of  making  objects  distinct.  This  point  is  clearly 
shown  by  places  where  all  objects  have  the  same  color,  as 
in  flour  mills;  diffused  light  here  would  give  results  that 
would  make  the  illumination  not  only  extremely  injurious 
to  the  eye,  but  absolutely  valueless  for  distinguishing  dif- 
ferent objects.  On  the  other  hand,  in  the  drafting  room, 
where  the  work  is  done  in  one  plane  only,  diffused  light 
is  required,  since  shadows  would  prove  very  troublesome 
to  the  draftsman. 


142  OIL  AND   GAS  LIGHTS 

SUMMARY 

A  Flame  is  a  vapor  or  a  gas  in  the  process  of  burning.  A 
burning  solid  produces  no  flame  unless  it  is  first  vaporized. 

A  Candle  is  composed  of  solid  fat  or  wax  molded  around  a 
wick. 

A  Kerosene  Lamp  has  a  reservoir  to  hold  the  oil,  a  wick  to  carry 
the  oil  to  the  burner,  a  burner  to  produce  a  thin  flame,  and  a 
chimney  to  increase  the  draft  of  air  through  the  burner. 

The  Flash  Point  of  an  oil  is  the  lowest  temperature  at  which  a 
mixture  of  its  vapor  with  air  will  burn  momentarily. 

Explosive  Mixtures  of  a  combustible  vapor  (or  gas)  and  air  are 
mixtures  which  burn  very  rapidly.  Their  range  of  composition 
varies  greatly  with  the  kind  of  vapor  or  gas  burned.  Air  contain- 
ing 10  %  to  66  %  of  hydrogen  or  with  from  3  %  to  30  %  of 
acetylene,  will  burn  explosively. 

Gasoline  Vapor  is  burned  to  produce  light,  heat,  and  power.  It 
has  a  wide  explosion  range. 

Gas  Burners  are  made  either  to  produce  a  thin,  luminous  flame, 
or  to  heat  a  mantle  to  incandescence.'  The  mantle  is  composed 
of  a  mixture  of  99  %  of  thorium  oxide  and  1  %  of  cerium  oxide. 

Acetylene  is  produced  by  the  reaction  between  water  and  cal- 
cium carbide. 

Prest-0-Lite  is  acetylene  dissolved  under  pressure  in  acetone. 
Blaugas  is  obtained  by  the  destructive  distillation  of  gas  9!!. 


EXERCISES 

1.  What  is  a  flame? 

2.  Does  pure  carbon  burn  with  a  flame  ?     Explain. 

3.  What  is  fractional  distillation  ? 

4.  What  are   some  of  the  products   obtained  by  the  frac- 
tional distillation  of  petroleum  ? 


EXERCISES  143 

5.  What  is  the  office  of  (a)  the  reservoir  of  a  kerosene 
lamp,  (6)  the  wick,  (c)  the  burner,  (d)  the  chimney? 

6.  How  does  the  Rochester  lamp  differ  from  the  ordinary 
lamp  ? 

7.  Define  flash  point. 

8.  What  is  the  minimum  legal  flash  point  of  kerosene  ? 

0 

9.  Would  an  explosion  follow  setting  fire  to  a  pail  of  gaso- 
line out  of  doors  ?     Explain. 

10.  Would  it  be  safe  to  allow  gasoline  to  evaporate  in  a 
room  containing  a  flame  ?     Explain. 

11.  What  is  meant  by  "  range  of  explosive  mixtures  "  ? 

12.  Will  any  mixture  of  illuminating  gas  and  air  explode 
when  ignited  ?     Explain. 

13.  What  are  some  of  the  methods  employed  for  the  pro- 
duction of  gasoline  vapor  for  use  as  an  illuminant  ? 

14.  What  causes  the  luminosity  of  the  ordinary  gas  flame  ? 

15.  Why  should  a  colorless  flame  be  used  with  a  Welsbach 
burner  ? 

16.  How  is  acetylene  made  ? 

17.  What  is  "  Prest-0-Lite  "  ? 

18.  Mention  two  advantages  and  two  disadvantages  in  the 
use  of  acetylene  as  an  illuminant. 

19.  What  is  "  Blaugas  "  ? 

20.  Mention  two  advantages  and  two  disadvantages  in  the 
use  of  "  Blaugas  "  as  an  illuminant. 


CHAPTER   XV 


-750 


AIR  AND  VENTILATION 

123.  Physical  Character  of  the  Air.  —  The  atmosphere 
may  best  be  thought  of  as  a  gaseous  ocean,  resting  on  the 
earth  and  held  in  place  by  gravity.  The 
air  exerts  a  pressure  of  14.7  pounds  on  every 
square  inch  of  area  at  the  sea  level.  As  we 
ascend,  the  pressure  becomes  less,  so  that 
the  exact  height  of  the  atmosphere  is  not 
known.  There  is,  however,  evidence  of  the 
existence  of  air  as  far  as  200  miles  from  the 
earth.  Changes  in  pressure,  due  to  local 
heating  of  the  air,  result  in  winds.  The 
barometer  (Fig.  55),  which  measures  these 
pressure  changes,  is  commonly  used  to  in- 
dicate probable  changes  in  the  weather. 

124.  Composition  of  Air.  —  The  important 
constituents  of  air  are  nitrogen,  oxygen,  water 
vapor,  carbon  dioxide,  together  with  a  mul- 
titude of  animate  and  inanimate  particles, 
constituting  bacteria  and  dust.  The  pro- 
portion of  oxygen  and  nitrogen,  which  to- 
gether make  about  99%  of  the  atmosphere, 
varies  to  a  slight  extent  in  town  and 
country,  indoors  and  out  of  doors.  The 
amount  of  water  vapor  present  depends  upon 
the  temperature  and  upon  the  available 
sources  of  water.  The  percentage  of  car- 
bon dioxide  is  affected  largely  by  the  decay 
144 


FIG.    55.  — 

BAROMETER. 


RELATION   TO  PLANT  AND  ANIMAL  LIFE     145 

of  animal  and  vegetable  matter,  by  the  presence  of 
numbers  of  people  and  by  fires  near  the  point  where  the 
air  is  collected  for  examination. 

125.  Air  a  Mixture.  —  Air  is  not  a  chemical  compound, 
but  simply  a  mixture  of  gases.     The  fact  that  its  compo- 
sition may  vary  is  one  proof  that  it  is  a  mixture.     Other 
proofs   include   the    following    facts.     It   is '  found   that 
when  air   dissolves   in  water,  the  dissolved  air   contains 
more  than  one-fifth  oxygen,  which  is  the  proportion  in 
normal  atmospheric  air.     By  the  application  of  cold  and 
pressure,  air  may  be  liquefied  and  even  solidified.     When 
liquid  air  evaporates,  the  nitrogen  boils  off  first,  finally 
leaving  nearly  pure  liquid  oxygen,  therefore  the  boiling 
point  of   the  liquid  air   is  not  constant.     If   air  were  a 
compound,  it  would  have  a  single  definite  boiling  point. 

126.  Relation  to  Plant  and  Animal  Life.  —  Both  plant  and 
animal  life  depend  upon  air  for  their  continuance.     Man 
and  all  other  animals  take  oxygen  from  the  air  by  means 
of  their  lungs  or  other  breathing  organs.     This  oxygen  is 
carried  by  the  blood  to  all  the  cells  of  the  body  and  unites 
with  the  carbon  and  hydrogen  of  which  the  cells  largely 
consist.     The  oxidation   of  the  cells  furnishes  the  heat 
necessary  to  keep  the  body  warm  and  the  energy  which 
enables  the  muscles  to  do  work.     The  products  of  oxida- 
tion are  carbon  dioxide  and  water: 

C       +    02    -+-   C02 

carbon         oxygen  carbon 

dioxide 

2H2    +    02    — ^2H20 

hydrogen      oxygen  water 

These  products  of  cell  oxidation  are  taken  up  by  the  blood 
and  eliminated  from  the  body  through  the  lungs,  skin,  and 


146  AIR   AND    VENTILATION 

kidneys.  Animals,  therefore,  reduce  the  amount  of  oxygen 
in  the  air  and  increase  the  proportion  of  carbon  dioxide 
and  water  vapor. 

Plants  breathe  also,  but  need  very  little  oxygen,  because 
their  movements  are  very  slight  and  so  a  small  amount  of 
energy  is  needed.  But  plants  are  constantly  growing 
and  their  tissues  also  consist  largely  of  carbon  and  hydro- 
gen. All  the  carbon  in  plants  comes  from  the  carbon  di- 
oxide in  the  air.  This  is  absorbed  by  the  leaves  and  in 
them  unites  with  the  water  taken  up  by  the  roots,  finally 
forming  sugar,  starch,  and  wood.  By  this  process,  the 
oxygen  of  the  absorbed  carbon  dioxide  is  liberated  and  re- 
turned to  the  air.  Plants,  therefore,  reduce  the  percentage 
of  carbon  dioxide  in  the  air  and  increase  the  percentage 
of  oxygen.  Decay,  fermentation,  and  fires  contribute 
largely  to  the  carbon  dioxide  in  the  air.  The  ease  with 
which  gases  diffuse  and  the  action  of  the  winds  greatly 
assist  in  maintaining  the  uniformity  of  the  atmosphere. 
Thus  we  see  that  natural  agencies,  working  together,  tend 
to  keep  the  proportion  of  oxygen  and  carbon  dioxide  in 
the  air  constant. 

127.  Ventilation.  —  In  buildings,  the  balance  of  oxygen 
and  carbon  dioxide  cannot  be  maintained  without  artificial 
aid  ;  hence  ventilation,  which  is  the  substitution  of  fresh 
air  for  contaminated  air,  is  necessary.  Pure  air  contains 
3  to  4  parts  of  carbon  dioxide  in  10,000 ;  when  this  is  in- 
creased in  rooms  to  30  or  40  parts  in  10,000,  with  a  cor- 
responding increase  in  water  vapor  and  other  emanations 
of  the  body,  the  air  becomes  close ;  then  breathing  is  no 
longer  comfortable.  When  we  consider  that  about  5% 
of  the  air  expelled  from  the  lungs  is  carbon  dioxide,  and 
that  lamps  and  gas  flames  return  to  the  air  a  volume  of 
carbon  dioxide  equal  to  the  volume  of  oxygen  consumed, 


VENTILA  TION 


147 


it  is  not  surprising  that  about  3000  cubic  feet  of  fresh  air 
per  hour  for  each  person  in  a  room  are  required  for  health. 

Rooms  are  not  perfectly  closed  boxes,  and  some  fresh 
air  finds  its  way  in  through  cracks  and  when  doors  are 
opened.  But  such  ventilation  is  not  sufficient,  particu- 
larly when  a  number  of  people  are  in  the  same  room. 
Open  fireplaces  aid  greatly  in  the  ventilation  of  rooms,  as 
fresh  air  finds  its  way  in  through  all  openings  and  cracks 
more  rapidly,  to  force  the  lighter  hot  air  up  the  chimney. 
When  the  fire  is  not  burning,  however,  cold  air  tends  to 
come  down  the  chimney,  pocketing,  near  the  ceiling,  the  im- 
pure heated  air  already  in  the  room  and  so  failing  to  pro- 
duce a  circulation  of  fresh  air.  It  is  well  to  keep  in  mind 
that  exhaled  air  from  the  lungs  and  the  waste  gases  from 
lamps  and  gas  burners  rise  because  their  temperature  makes 
them  lighter,  although  the  carbon  dioxide  in  them  is 
heavier  than  pure  air  at  the  same  temperature. 

The  amount  of  leakage  around  windows  and  doors  and 
through  the  walls  of  a  room  is  sufficient  to  change  the  air 
about  once  an  hour  in  winter  weather.  To  secure  addi- 
tional ventilation,  fresh  air  must  be  admitted  and  foul  air 
allowed  to  escape,  without  causing  drafts.  When  a  house 
is  heated  by  a  properly  de- 
signed and  well-managed 
hot-air  furnace,  this  does 
much  to  promote  circula- 
tion, and  has  the  additional 
advantage  of  warming  the 
incoming  air.  Houses 
otherwise  heated  secure  a 
considerable  amount  of 
fresh  air  by  the  opening  of 

the  OUtside    door    aS    people      courtesy  of  The  Scientific  American. 

pass  in  and  out.      Usually     FIG.  56.  —  INDIRECT  HEATING  SYSTEM. 


148 


AIR  AND    VENTILATION 


this  is  not  enough.  Systems  of  combined  heating  and 
ventilation  have  been  devised  in  which  hot  water  or 
steam  radiators  are  placed  in  boxes  provided  with  an 
inlet  for  fresh  air  from  outdoors,  and  an  outlet  for 
discharging  the  heated  fresh  air  into  the  room  (Fig. 
56).  This  method  is  efficient  as  far  as  furnishing  properly 
warmed  fresh  air  is  concerned,  but  is 
wasteful  of  fuel  in  times  of  high  winds 
and  cold  weather. 

When  windows  are  used  for  ventila- 
tion, they  should  be  opened  at  both  top 
and  bottom,  if  the  weather  permits,  or 
in  any  case  at  the  top.  The  cold  air 
will  force  its  way  in  through  the  bottom 
opening,  or  up  between  the  sashes,  and 
drive  out  the  warm,  foul  air  easily  and 
directly  through  the  opening  at  the  top 
(Fig.  57).  If  the  window  is  opened 
at  the  bottom  as  well  as  at  the  top,  drafts 
should  be  avoided  by  deflecting  the  in- 
coming cold  air,  so  that  it  will  flow  up 
the  sash  a  little  way,  and  not  blow  hori- 
zontally into  the  room.  The  windows  of 
sleeping  rooms  should  always  be  opened 
top  and  bottom,  the  amount  of  opening 
being  suited  to  weather  conditions. 

Halls,  churches,  schools,  theaters,  tene- 
ment and  apartment  houses,  and  all 
other  places  where  a  large  number  of  people  gather 
in  a  comparatively  small  space,  require  special  ven- 
tilation. Fresh  warmed  air  should  be  distributed  to 
each  room  through  a  definite  flue  and  the  foul  air 
removed  through  another  flue.  Positive  means  of  se- 
curing circulation,  such  as  a  blower  to  drive  the  fresh  air 


FIG.  57.  —  AIR 
CURRENTS  AT  AN 
OPEN  WINDOW. 


CARBON  DIOXIDE  149 

over  heating  coils  and  into  the  rooms,  and  another  blower 
to  draw  the  foul  air  out  of  the  rooms,  should  be  adopted 
in  schools  and  public  buildings. 

128.  Nitrogen.  —  Nitrogen,  comprising  nearly  four  fifths 
of  the  air,  is  the  largest  constituent  of  the  atmosphere. 
It  is  an  inert  gas,  that  is,  it  does  not  support*  combustion 
and  does  not  readily  unite  with  other  elements.     Nitrogen 
dilutes  the  oxygen  in  the  air  and  thus  lessens  the  speed  of 
oxidation.      Nitrogen  cannot  be  directly  assimilated   by 
animals  nor  by  plants  in  general,  yet  nitrogen  is  an  im- 
portant constituent  of  all  living  bodies.     Protoplasm,  the 
essential  substance  in  living  tissues,  is  a  very  complex 
compound  containing  nitrogen.     Meat  and  the  white  of 
egg  are  examples  of  substances  particularly  rich  in  nitro- 
gen.    Animals  are  compelled  to  depend  upon  plants  or 
upon  the  flesh  of  other  animals  for  their  nitrogen  com- 
pounds.    Plants,  however,  can  manufacture  protoplasm  in 
their  cells,  taking  simple  nitrogen  compounds  from  the 
soil  through  their  sap.     Thus,  in  time,  the  nitrogen  of  the 
soil  becomes  exhausted,  and  nitrates  or  other  compounds 
of   nitrogen   must    be    used   as    fertilizers     (see    Chap. 
XLV).       Nitrogen  is   also   an  important   constituent  of 
explosives. 

Associated  with  nitrogen  and  distinguished  from  it 
only  a  few  years  ago,  are  other  gases  resembling  nitrogen. 
Argon  is  the  chief  of  these  inert  gases,  which  together 
form  about  1  %  of  the  air.  They  form  no  compounds  and 
seem  to  be  without  chemical  activity. 

129.  Carbon  Dioxide.  —  The  presence  and  proportion  of 
carbon  dioxide  in  the  air  has  already  been  mentioned.     It 
is  an  odorless  gas,  about  one  and  a  half  times  as  heavy  as 
air.     The  most  marked  characteristic  of  carbon  dioxide  is 


150  AIR  AND    VENTILATION 

that  it  will  neither  support  combustion  nor  life.  Where 
ventilation  does  not  take  place  readily,  as  in  caves  and  wells, 
the  carbon  dioxide  formed  from  decay  or  as  a  result  of 
decomposition  going  on  in  the  earth,  sometimes  accumu- 
lates, displacing  the  normal  air.  Before  entering  such 
places  for  any  purpose  one  should  test  them  with  a  burn- 
ing candle.  If  the  candle  continues  to  burn  brightly,  it  is 
safe  to  enter ;  otherwise  suffocation  might  result. 

The  usual  test  for  the  purity  of  air  is  to  determine  the 
percentage  of  carbon  dioxide  in  it.  This  is  because  the 
amount  of  carbon  dioxide  produced  by  breathing  or  by  fires 
serves  as  an  index  to  the  amount  of  other  impurities,  which 
are  present  in  smaller  amounts  and  are  more  difficult  to 
determine.  The  unpleasant  effects  in  crowded  rooms  of  air 
containing  less  than  1  %  of  carbon  dioxide  is  probably  due 
in  large  measure  to  the  presence  of  these  other  impurities 
and  of  water  vapor.  This  is  shown  by  the  fact  that  in 
factories  where  carbon  dioxide  is  made  for  charging  soda 
fountains  and  mineral  water,  the  air  may  contain  much 
more  than  1  %  of  carbon  dioxide  without  any  unpleasant 
effect  being  experienced. 

130.  Water  Vapor.  —  Water  vapor  is  always  present  in 
the  air,  even  in  desert  climates,  but  the  proportion  which 
air  may  contain  before  becoming  saturated  depends  upon 
the  temperature.  While  air  at  32°  F.  can  hold  less  than 
5  grams  of  water  to  the  cubic  meter  without  precipitating 
it  in  the  form  of  rain  or  snow,  air  at  60°  F.  can  hold  nearly 
13  grams,  and  air  at  90°  F.  about  34  grams  of  water  vapor 
per  cubic  meter  before  becoming  saturated.  The  cloud 
of  water  dust  seen  when  we  exhale  on  a  cold  day  is  due 
to  the  fact  that,  while  the  air  from  the  lungs  is  not 
saturated  at  the  temperature  of  the  body,  it  is  more 
than  saturated  at  the  temperature  of  the  surrounding 


HUMIDITY  OF   THE  AIR  151 

atmosphere.     The  frost  on  windows  is  caused  in  a  similar 
manner. 

The  amount  of  water  vapor  present  in  the  air  reaches 
the  saturation  point  only  when  it  is  rainy  or  foggy.  On 
a  clear  day  the  proportion  may  be  only  30  or  40  %  of 
the  amount  needed  for  saturation.  The  evaporation  of 
perspiration  from  the  skin  depends  not  only*  on  the  tem- 
perature of  the  air,  but  also  on  the  amount  of  vapor  al- 
ready present  in  the  air.  When  the  atmosphere  is  nearly 
saturated  with  water,  evaporation  is  checked,  and  we  be- 
come uncomfortable.  This  probably  accounts  largely  for 
the  discomfort  of  crowded  rooms,  as  noted  above.  On  the 
other  hand,  if  there  is  very  little  vapor  in  the  air,  evapora- 
tion is  too  rapid.  This  is  the  usual  condition  of  buildings 
heated  by  any  of  the  ordinary  methods ;  their  climate  is 
that  of  the  desert.  This  may  be  remedied  by  providing  a 
supply  of  water  so  located  that  it  may  readily  evaporate 
into  the  air  supply  of  the  room. 

131.  Relative  Humidity.  —  The  quotient  obtained  by  di- 
viding the  amount  of  vapor  actually  present  by  the  amount 
necessary  for  saturation  at  the  observed  temperature,  is 
the  relative  humidity.     A  humidity  of  about  60  %  is  nearly 
right  for  comfort.     On  a  hot,  muggy  day  the   relative 
humidity  is  very  high,  evaporation  is  checked,  and  we 
feel  uncomfortable  and  out  of  sorts.     The  bracing  quality 
of   a  cool,  dry  day  is  due   largely  to  the   low  relative 
humidity. 

132.  Dust  and  Bacteria.  —  In  addition  to  the  gaseous 
substances    already   discussed,    the    air    always    contains 
great  numbers  of  solid  particles  small  enough  to  be  blown 
about  by  the  winds,  and  so  small  that  they  settle  very 
slowly,  even  through  perfectly  still  air.     The  larger  ones 


152 


AIR  AND    VENTILATION 


can  be  both  seen  and  felt  as  dust  particles ;  smaller  ones 
are  the  motes  which  show  the  path  of  a  beam  of  light 
through  a  room  ;  and  still  smaller  ones  are  revealed  when 
an  undusted  object  is  examined  with  a  microscope.  The 
name  "  dust "  is  usually  applied  to  all  such  particles,  but 
it  might  better  be  limited  to  mineral  particles  and  dead 
organic  matter.  The  number  of  particles  of  dust  in  a 
cubic  inch  may  range  from  2000  in  the  open  country  to 
30,000,000  in  an  occupied  room.  A  very  large  propor- 
tion of  the  latter  num- 
ber are  not  dead  matter, 
but  are  the  tiny  living 
organisms  called  bac- 
teria, germs,  microbes, 
etc.  These  are  usually 
single-celled,  "  living 
bodies,  capable  of  re- 
producing themselves 
with  enormous  rapidity 
when  they  find  suitable 
conditions.  These  con- 
ditions include  warmth, 
moisture,  and  suitable  food  material.  Fermentation  and 
decay  are  produced  by  the  action  of  bacteria,  since  animal 
and  plant  material,  living  or  dead,  affords  the  proper  con- 
ditions for  their  growth  and  reproduction. 

In  the  case  of  many  contagious  diseases,  the  particular 
variety  of  bacteria  associated  with  the  disease  has  been 
identified  and  the  treatment  adopted  is  designed  to  destroy 
these  bacteria.  Many  forms  of  bacteria,  such  as  that  caus- 
ing consumption,  may  dry  up  and  remain  without  appar- 
ent life  for  long  periods,  and  then  become  active  as  soon 
as  the  proper  conditions  are  provided. 

It  will  be  seen,  from  this  very  brief  statement  of  the 


Magnified  40  diameters. 

FIG.    58.  —  PHOTOMICROGRAPH    OF    DUST 
IN  AIR. 


OTHER    CONSTITUENTS  OF  AIR  153 

constitution  of  dust,  how  important  it  is  to  avoid  breath- 
ing more  dusty  air  than  we  can  possibly  help.  Every 
precaution  should  be  taken  in  the  case  of  germ  diseases 
to  prevent  the  escape  of  the  germs  and  so  cause  the  disease 
to  spread.  A  sheet  kept  moist  with  a  disinfectant  solu- 
tion.—  that  is,  one  which  will  kill  injurious  bacteria  — 
and  hung  before  the  door  of  a  sick  room,  helps  very  much 
to  prevent  the  spread  of  germs  through  the  air  to  other 
rooms.  Fumigation  of  a  room  in  which  there  has  been  a 
case  of  contagious  disease  by  gaseous  disinfectants,  such 
as  formaldehyde,  or  sulphur  dioxide,  is  for  the  purpose  of 
destroying  the  germs  in  the  air  as  well  as  those  which 
have  settled. 


A  B  CD 

Courtesy  of  the  American  Museum  of  Natural  History. 

FIG.  59.  —  BACTERIA  FOUND  IN  AIR  (MAGNIFIED  4000  DIAMETERS). 

A,  Bacillus  of  tuberculosis;    B,  Bacillus  of  diphtheria;     C,  Diplococcus 
of  pneumonia ;    D,   Bacillus  of  influenza. 

133.  Other  Constituents  of  Air.  —  Other  gases  which  are 
present  in  the  air  in  small  amounts  are  nitric  acid, 
ammonia,  and  ozone.  The  nitric  acid  is  formed  by  the 
solution  of  nitrogen  oxides  in  the  moisture  of  the  upper 
atmosphere.  These  nitrogen  oxides  are  formed  by  the 
combination  of  nitrogen  and  oxygen  when  the  air  is  highly 
heated  by  the  passage  of  a  flash  of  lightning.  The  ammo- 
nia is  chiefly  the  result  of  the  decomposition  of  organic 
matter  containing  nitrogen ;  its  odor  is  noticeable  in 
stables  and  other  places  where  such  decomposition  is  tak- 
ing place.  By  diffusion,  ammonia  is  distributed  through- 
out the  atmosphere.  Both  ammonia  and  nitric  acid  are 
washed  out  of  the  air  during  rain  storms  and  so  help  to 
restore  nitrogen  to  the  soil. 


154  AIR  AND    VENTILATION 

Ozone  is  a  more  active  form  of  oxygen.  It  is  a  gas  with 
a  penetrating  odor,  and  is  always  formed  when  electric 
sparks  are  passing  through  the  air.  During  thunder  storms 
it  is  produced  in  considerable  quantities  and  probably  con- 
tributes to  the  invigorating  quality  of  the  air  immediately 
after  a  storm.  This  quality  of  air  is  also  due  to  the. fact 
that  the  rain  washes  the  dust  and  smoke  out  of  the  air, 
leaving  it  clearer  and  more  transparent.  Ozone  is  known 
to  be  a  good  bleaching  agent  and  disinfectant,  and  the 
bleaching  of  cloth  spread  on  the  grass  is  commonly  be- 
lieved to  be  caused  by  ozone.  Ozone  is  also  found  where 
waves  are  beaten  into  surf  on  the  shore  and  it  contributes 
to  the  invigorating  quality  of  sea  air.  Other  gases  and 
impurities  are  present  in  the  air  in  certain  localities,  but 
they  are  only  found  locally  and  so  we  need  not  consider 
them. 

SUMMARY 

The  Chief  Constituents  of  air  are  nitrogen  and  oxygen,  mixed 
in  the  proportion  of  about  4  parts  of  nitrogen  to  1  of  oxygen.  Air 
is  not  a  chemical  compound.  Water  vapor  and  carbon  dioxide 
are  other  important  constituents  of  air. 

Animals,  in  breathing,  take  oxygen  from  the  air  and  give  carbon 
dioxide  to  it. 

Plants,  in  the  formation  of  starch,  take  carbon  dioxide  from 
the  air  and  give  oxygen  to  it. 

Air  in  Rooms  must  be  constantly  renewed,  in  order  to  remove 
the  waste  gases  exhaled  and  to  renew  the  supply  of  available 
oxygen.  Good  ventilation  requires  constant  change  of  air,  with- 
out draughts. 

Nitrogen  is  a  gas  which  does  not  react  readily  with  other  ele- 
ments. It  is  an  essential  constituent  of  all  living  bodies. 


EXERCISES  155 

Carbon  Dioxide  will  support  neither  combustion  nor  life.  The  per- 
centage of  carbon  dioxide  in  air  serves  as  an  index  of  the  total 
impurities  present. 

The  percentage  of  Water  Vapor  in  air  is  constantly  changing, 
and  affects  the  climate  and  also  human  comfort. 

Dust  in  the  air  always  contains  bacteria,  and  so  every  pre- 
caution should  be  taken  to  avoid  breathing  dust  and  to  protect 
food  from  it. 

Other  constituents  of  the  air  include  nitric  acid,  ammonia, 
and  ozone. 

EXERCISES 

1.  Name  four  constituents  of  air  and  state  the  importance 
of  each  to  man. 

2.  Give  two  proofs  that  air  is  a  mixture  and  not  a  compound. 

3.  Show  how  plants  and  animals  depend  on  each  other  for 
existence. 

4.  Why  is  oxygen  necessary  for  animal  life  ? 

5.  State,  with  reasons,  the  best  way  of  ventilating  your 
sleeping  room. 

6.  Discuss  fireplaces  as  a  means  of  ventilation. 

7.  Would  a  person  die  if  shut  up  in  a  room  with  the  doors 
and  windows  closed  ?     Explain. 

8.  Why  do  schools  require  more  systematic  ventilation  than 
houses  ? 

9.  Compare  nitrogen  with  oxygen  in  its  chemical  activity. 
In  its  importance  to  man. 

10.  Why  are  nitrogen  compounds  of  great  importance  in 
fertilizers  ? 

11.  Why  are  we  more  uncomfortable  when  the  humidity  is 
high  than  when  it  is  low  ? 


156  AIR   AND    VENTILATION 

12.  Why  is  the  air  chamber  of  a  hot-air  furnace  provided 
with  a  pan  for  water  ? 

13.  Show  the  relation  of  bacteria  to  dust  and  to  disease. 

14.  Why  is  vacuum  cleaning  more  sanitary  than  sweeping  ? 

15.  What  is  ozone?     How  is  it  produced?     What  are  its 
uses  ? 

16.  Compare  steam  heat  and  furnace  heat  as  aids  to  the  ven- 
tilation of  a  house.     How  do  these  two  systems  affect  the 
humidity  of  the  air  in  the  rooms  ? 


CHAPTER  XVI 

• 

CHEMICAL  PURIFICATION 

134.  Chemical  Purity.  —  Granulated  sugar  and  starch  are 
two  substances  which  come  into  the  household  in  a  high 
state  of  purity.     Nearly  everything  else  that  we  see  or 
use  is  a  mixture  which  bears  the  name  of  the  dominant 
material,  but  which  contains  many  others.     The  minor 
constituents  are  usually  not  objectionable,  and  are  allowed 
to  remain  because  the  process  of  removing  them  is   too 
expensive.     In  the  case  of  sugar,   although   the  natural 
impurities  that  are  present  in  the  first  stages  of.  the  man- 
ufacturing process  would  do  no  great  harm,  we  get  the 
article  in  a  pure  state  because  the  public  likes  it  to  be 
crystalline  in  appearance.       Furthermore,  the  process  of 
purification  is  not  very  expensive. 

For  much  chemical  work,  a  state  of  purity  comparable 
to  that  of  starch  and  of  sugar  is  desirable  ;  it  is  essential  in 
all  that  involves  analysis  or  a  study  of  properties.  Hence 
the  processes  of  purification  are  an  important  part  of  a 
chemist's  knowledge.  High  degrees  of  purity  are  dif- 
ficult to  obtain,  and  absolute  purity  is  wholly  a  theo- 
retical matter.  Even  water  has  never,  in  all  proba- 
bility, been  obtained  in  a  state  of  perfect  purity. 

135.  Purification  of  Gases. — As  a  rule,  impurities  are 
removed   from   gaseous   mixtures   by  means  of  chemical 
action.     The  gases  are  passed  through  liquids   or   over 
solids  that  will  react  with  the  impurity.     Hydrogen  sul- 

157 


158  CHEMICAL   PURIFICATION 

phide  is  removed  from  illuminating  gas  by  passing  it  over 
moist  iron  oxide.  Carbon  dioxide  can  be  removed  from 
other  gases  by  passing  the  mixture  through  a  solution  of 
potassium  hydroxide,  or  over  sticks  of  the  solid  substance. 
Water  vapor  is  absorbed  by  passing  the  moist  gas  through 
concentrated  sulphuric  acid,  or  over  lumps  of  anhydrous 
calcium  chloride. 

Pure,  dry  hydrogen  is  obtained  by  passing  the  gas  from 


tiMy 

m  m  i 


a 
FIG.  60.  —  PURIFICATION  OF  HYDROGEN. 

the  generator  (Fig.  60,  a)  through  an  acid  solution  of  po- 
tassium permanganate  (6)  to  remove  hydrogen  sulphide, 
and  through  concentrated  sulphuric  acid  (c  and  d)  to  re- 
move water  vapor. 

136.  Purification  of  Liquids  by  Distillation.  —  If  a  liquid 
contains  a  dissolved  impurity,  whether  the  latter  be  a 
solid,  liquid,  or  gas,  the  process  of  boiling,  or  of  boiling 
and  condensation,  is  usually  employed  to  bring  about  a 
separation.  Gases  are  less  soluble  in  hot  than  in  cold 


rUltlFlCATLON  OF  LIQUIDS  BY  DISTILLATION     159 


liquids,  and  continued  boiling  will  therefore  drive  out  a 
gas  from  a  liquid  solvent. 

If  the  dissolved  impurity  is  itself  a  liquid,  the  solution 
is  boiled  and  the  gases  that  come  off  are  led  through  a 
tube  that  is  surrounded  by  cold  water,  whereby  they  are 
condensed  and  again  become  liquids  (Fig.  61).  This 
double  process  is  called  distillation.  Since  every  chemical 


FIG.  61.  —  LABORATORY  DISTILLATION. 

compound  that  will  endure  distillation  without  decompo- 
sition has  its  own  definite  and  constant  boiling  point,  the 
constituents  of  the  liquid  mixture  tend  to  come  off  at 
different  temperatures  during  the  heating.  The  boiling 
begins  at  a  temperature  near  that  required  for  the  boiling 
of  the  constituent  having  the  lowest  boiling  point,  and  the 
condensed  liquid  will  at  first  consist  mostly  of  this  more 
volatile  substance.  In  distilling  a  mixture  of  alcohol  and 
water,  for  example,  the  boiling  begins  near  80°,  and  the 


160  CHEMICAL  PURIFICATION 

temperature  gradually  rises  to  over  100°  C.  The  first  part 
of  the  liquid  that  condenses,  the  distillate,  is  largely  alcohol, 
but  it  contains  some  water;  the  last  part-of  the  distillate 
is  water  containing  a  little  alcohol. 

Using  this  principle,  a  mixture  of  two  liquids  can  be 
separated  to  a  greater  or  less  extent.  If  the  boiling  points 
lie  close  together,  as  in  the  case  of  alcohol  and  water,  re- 
peated distillation  is  necessary,  and  a  complete  separation 
cannot  be  effected  by  distillation  alone.  If  the  boiling 
points  lie  far  apart,  the  separation  is  easier.  There  are 
a  few  cases  where  a  mixture  will  boil  at  a  constant  tem- 
perature, provided  the  pressure  remains  the  same,  and  will 
give  a  distillate  of  definite  composition,  for  example,  a 
mixture  of  acetic  acid  and  water,  or  a  mixture  of  nitric 
acid  and  water. 

When  liquids  contain  dissolved  solids,  the  liquid  can 
almost  always  be  distilled  and  a  nearly  perfect  separation 
easily  effected. 

In  many  kinds  of  chemical  manufacturing,  distillation 
is  an  essential  part  of  the  process  and  is  carried  out  on  a 
very  large  scale.  By  such  a  process,  we  get  from  crude 
petroleum  many  different  products  such  as  naphtha,  gaso- 
line, kerosene,  and  lubricating  oils. 

137.  Purification  of  Liquids  by  Freezing.  —  When  a  solu- 
tion  is  frozen,  the  solvent  separates  as  a  comparatively 
pure  substance.     Hence,  if  a  liquid  mixture  is  cooled  to 
the  freezing  point  of  the  solvent,  as  the  latter  gradually 
solidifies,  the  impurity  will  remain  in  the  unfrozen  part 
of  the  solution.     When  brine  freezes,  the  ice  that  forms 
is  practically  free  from  salt.     This  process  often  affords  a 
convenient  means  of  purification. 

138.  Purification  of  Solids.  —  Distillation  may  also  be  used 
as  a  means  of  purifying  solids,  provided  the  solid  does 


WASHING  AND   FILTRATION 


161 


not  change  chemically  in  being  heated  to  its  boiling  point. 
Many  solids  are  commercially  refined  in  this  way. 
Among  them  are  sulphur,  camphor,  iodine,  and  even  the 
metal  zinc.  The  process  is  called  sublimation  when  the 
condensed  substance  is  deposited  as  a  solid.  More  com- 
monly, in  the  purification  of  solids,  other  processes  are 
utilized  that  depend  upon  solution,  washing,  precipitation, 
filtration,  and  crystallization.  All  chemical  manufactur- 
ing involves  a  large  amount  of  this  work. 


139.  Washing  and  Filtration.  —  Filtration  may  be  one  of 
two  operations :  (a)  the  straining  out  of  a  solid  from  a 
liquid  by  passing  the 
liquid  through  a  porous 
substance  such  as  paper 
or  cloth,  the  solid  re- 
maining on  the  filter- 
ing surface  ;  (6)  passing 
a  solution  through  a 
thick  layer  of  powdered 
material,  such  as  animal 
charcoal,  which  will  ab- 
sorb impurities  that  are 
in  solution.  Washing 
is  practically  a  filtra- 
tion in  which  the  solid 
substance  to  be  purified 
is  placed  on  a  porous 
substance,  and  the  im- 
purities washed  out  by 
treating  with  a  suitable 
liquid,  which  drains 
through,  carrying  the  impurities  with  it  (Fig.  62). 
The  first  operation  in  the  refining  of  raw  sugar  is  a  pro- 


FIG.  62. — WASHING  A   PRECIPITATE  ON  A 
SUCTION  FILTER. 


162 


CHEMICAL   PURIFICATION 


cess  of  this  sort.     In  this  case,  and  in  many  other  man- 
ufacturing operations,  the  process  is  greatly  hastened  by 

the  use  of  centrifugal  filters. 
These  are  large  pans  with  many 
fine  perforations  in  the  sides 
(Fig.  63,  £>),  capable  of  being 
rotated  in  a  horizontal  plane 
with  great  velocity.  The  liquid 
part  of  any  mixture  that  is  put 
in  them  is  thrown  off  with  great 
rapidity  and  completeness  by 
centrifugal  action.  A  later  op- 
eration in  the  purification  of 
sugar  consists  in  passing  it  in 
solution  through  a  very  thick 
layer  of  bone  charcoal.  This 
represents  the  second  kind  of 
filtration  described  above.  Im- 
purities that  would  give  the  sugar  a  brown  color  are 
absorbed  by  the  charcoal,  and  the  solution  comes  through 
nearly  colorless. 

140.  Precipitation.  —  This  operation  can  often  be  used  as 
a  means  of  purification.  When  an  insoluble  substance  is 
formed  within  a  solution  by  either  physical  or  chemical 
action,  it  separates  as  a  definite  chemical  compound,  and 
other  substances  remain  in  solution.  The  precipitated 
material  has  merely  to  be  filtered  off  and  washed,  to  be 
obtained  in  a  high  state  of  purity.  An  application  of  this 
principle  will  give  a  form  of  common  salt  so  pure  that  it 
will  not  deliquesce.  Ordinary  salt  is  dissolved  in  the 
least  quantity  of  water  that  will  suffice,  and  hydrogen 
chloride  is  added.  The  sodium  chloride,  being  much  less 
soluble  in  a  solution  of  hydrochloric  acid  than  in  water, 


FIG.  63. — CENTRIFUGAL  FILTER. 

a,  outer  drum  ;  b,  perforated 

drum. 


CR  YSTALLIZA  TION 


163 


separates  as  crystals.     The  disturbing  impurity,  magnesium 
chloride,  is  left  in  the  solution. 

141.  Crystallization.  —  Crystallization  is  a  term  used  to 
indicate  a  kind  of  slow  precipitation  in  which  the  substance 
that  separates  assumes  a  regular  and  symmetrical  form 
(Fig.  64).  It  is  brought  about  by  a  change  in  the  physi- 
cal condition  of  the  solvent,  usually  a  lowering  of  its  tem- 


FIG.  64. — TYPICAL  CRYSTALS. 
a,  K2S04;  b,  K2S04  Cr2(S04)3.24  H20  ;  c,  CuS04.5  H2O. 

perature  or  a  diminution  of  its  volume.  Impurities,  if 
present,  remain  in  the  solvent,  as  does  a  part  of  the  solute. 
This  remaining  liquid  portion  is  called  the  mother  liquor. 
For  purposes  of  purification,  it  is  desirable  to  have  the 
individual  crystals  as  small  as  possible.  This  result  is  ob- 
tained by  stirring  the  mixture  thoroughly  while  the  crys- 
tals are  forming.  There  is  always  a  tendency  for  the 
crystal  to  retain  within  itself  a  certain  amount  of  mother 
liquor ;  but  if  the  crystal  is  small,  there  is  less  chance  of 
this  contamination.  Since  it  cannot  be  altogether  avoided, 


164  CHEMICAL   PURIFICATION 

a  single  crystallization  may  not  give  a  very  high  grade  of 
purity.  As  with  the  separation  of  liquids  by  distillation, 
several  repetitions  of  the  process  are  frequently  employed, 
and  we  speak  of  the  process  as  r  eery  stabilization.  After 
the  crystals  are  formed,  they  are  separated  from  the 
mother  liquor  by  filtration,  and  perhaps  washed  with  a 
small  quantity  of  the  pure  solvent.  The  final  operations 
in  the  purification  of  sugar  are  those  of  recrystallization. 


SUMMARY 

Chemical  Compounds,  even  tolerably  free  from  other  substances, 
are  not  easily  prepared.  High  degrees  of  purity  are  secured  only 
after  repeated  operations,  and  absolute  purity  does  not  exist.  Sugar 
and  starch  are  two  substances  that  come  into  the  house  in  a  high 
state  of  purity. 

Gases  are  purified  by  bringing  them  into  contact  with  liquids  or 
with  solids  that  will  react  chemically  with  the  impurities. 

Distillation  is  a  process  that  includes  two  operations :  first,  the 
converting  of  liquids  or  solids  into  gases  by  heat ;  second,  the  cool- 
ing of  these  gases  until  they  again  assume  a  liquid  or  solid  form. 
If  the  cooled  substance  is  deposited  immediately  as  a  solid,  the 
process  is  termed  sublimation. 

Distillation  and  sublimation  are  important  methods  of  purification. 
The  principle  underlying  the  methods  is  that  different  chemical 
compounds  are  converted  into  gases,  each  at  its  own  definite  and 
characteristic  temperature.  Mixtures  of  mutually  soluble  liquids 
do  not  boil  exactly  according  to  this  principle  ;  the  boiling  begins  at 
a  temperature  near  that  required  for  the  boiling  of  the  constituent 
having  the  lower  boiling  point,  and  in  most  cases  the  temperature 
then  rises  gradually  to  or  above  that  required  for  the  constituent 
having  the  higher  boiling  point.  The  substance  that  comes  off  (the 
distillate)  is  a  mixture  of  the  two  liquids  in  varying  proportion. 


EXERCISES  165 

Repeated  distillation  is  necessary  to  separate  a  mixture  of  such 
liquids. 

Gases  are  less  soluble  in  hot  than  in  cold  liquids. 

When  a  solvent  freezes,  dissolved  substances  that  are  present 
are  precipitated,  or  remain  dissolved  in  the  unfrozen  part  of  the 
solution. 

Filtration  and  Washing  are  used  to  separate  insoluble  solids 
from  soluble  ones.  Filtration  also  includes  purification  by  absorp- 
tion of  soluble  impurities  from  -  solutions  as,  for  example,  decolori- 
zation  of  sugar  sirup  by  charcoal.  .Centrifugal  filters  permit  very 
rapid  filtration  and  washing. 

Precipitation  occurs  when  an  insoluble  solid  is  formed  within  a 
solution,  or  when  a  condition  of  insolubility  for  a  substance  has 
been  established  in  a  solution.  Such  a  precipitated  substance  can 
be  obtained  in  a  pure  state  by  filtering  it  from  the  solution  and 
washing. 

Crystallization  is  a  kind  of  precipitation  in  which  the  solid 
separates  more  or  less  slowly  and  in  doing  so  assumes  a  regular 
geometric  form.  It  may  be  used  as  a  means  of  purification  for 
the  same  reasons  that  precipitation  may  be  so  used.  Repetitions 
of  the  process  are  necessary  to  secure  any  high  degree  of  purity. 


EXERCISES 

1.  Why   is  not  chemical  purity   necessary   for    most   pur- 
poses ?     Distinguish  between  water  that  is  chemically  pure, 
and  water  that  is  hygienically  pure. 

2.  How  would  you  remove  hydrogen  sulphide  (a  gas)  from 
water  in  which  it  was  dissolved  ?     Explain. 

3.  How  could  you  separate  sugar  from  earth  or  sand  and 
save  the  sugar  ? 

4.  How  would  you  separate  oxygen  from  air  so  as  to  ob- 
tain nitrogen  ? 


166  CHEMICAL  PURIFICATION 

5.  How  would  you  obtain  dry  air  for  a  chemical  experi- 
ment ? 

6.  Define     distillation,    sublimation,    crystallization,    re- 
crystallization,  and  filtration. 

7.  How  would  you  obtain  pure  water  and  pure  salt  from 

brine  ? 

• 

8.  Describe  what  happens  when  a  mixture  of  alcohol  and 
water  is  distilled. 

9.  How  could  gasoline  that  had  been  used  to  clean  clothing 
be  recovered  in  a  pure  state  ?     What  sources  of  danger  attend 
this  operation? 

10.  If   a  solution  containing   sodium  chloride,  water,  and 
ammonia  gas  were  distilled,  what  would  happen  ? 

11.  In  the  cold  parts  of  Russia,  salt  is  obtained  from  sea 
water  by  freezing.     What  principle  is  involved  ?     How  would 
the  operation  be  carried  out  ? 

12.  Describe  the  action  of  centrifugal  filters. 

13.  Why  is  bone  charcoal  used  in  the  purification  of  sugar  ? 

14.  Which  would  taste  salter,  sea  water  or  water  resulting 
from  the  melting  of  sea  ice  ?     Why  ? 

15.  Define  precipitation.     Why  can  it  be  used  as  a  means 
of  purification  ? 

16.  How  could  you  obtain  pure  sodium  chloride  from  a  so- 
lution that  also  contained  a  little  potassium  nitrate  ? 

17.  How  would  you  proceed  in  order  to  get  large  crystals 
from  a  solution  ?     Small  ones  ?     Which  would  be  better  if  you 
were  using  crystallization  as  a  means  of  purification  ? 


CHAPTER   XVII 
WATER 

142.  Value  of  Water.  —  Every  one  understanding  the 
life  processes  of  plants  and  animals  fully  realizes  the  im- 
portance of  water.       With  the  increase  of  population,  the 
struggle  to  secure  a  sufficient  supply  of  pure  and  whole- 
some water  has  become  a  most  vital  problem  of  the  pres- 
ent day.     Only  within  the  last  twenty  years  have  Ameri- 
can communities  realized  the  value  of  pure  water  in  con- 
serving the  health  of  the  people  and  in  promoting  their 
prosperity. 

143.  Sources  of  Water. — The  sources  of  water  supply 
may  be  classed  in  two  divisions,  surface  waters  and  ground 
^vaters.     The   surface   waters  include  the  rain  collected 
from  roofs,  river  waters,  water  in  natural  lakes,  and  the 
water  collected  from  watersheds  in  reservoirs.     Ground 
waters  comprise  the  waters  of  springs,  wells,  and  under- 
ground chambers  or  galleries.     The  source  selected  for  a 
town  or  city  supply  depends  mainly  on  two  factors,  —  the 
quantity  and  the  quality  of  the  water.     The  quality  is  de- 
termined by  substances  either  dissolved  or  suspended  in 
the  water. 

144.  Content  of  Natural  Waters.  —  As   a   result   of  the 
intimate  association  with  life  and  other  natural  processes, 
surface  and  ground  waters  contain  a  wide  variety  of  sub- 
stances.    These  may  be  roughly  classified  according  to 

167 


168  WATER 

their  origin,  as  organic  and  inorganic.  The  organic  mate- 
rials are  derived  from  animal  and  vegetable  life.  After  the 
death  of  living  matter,  bacterial  processes  of  putrefaction 
and  decay  disintegrate  the  tissues.  The  products  of  de- 
composition either  blend  with  the  soil  already  formed,  or 
escape  into  the  air  as  gaseous  substances,  such  as  ammonia, 
nitrogen,  or  carbon  dioxide.  As  water  mingles  with  the 
soil,  it  not  only  takes  up  the  products  of  decomposition  of 
organic  matter,  but  also  countless  numbers  of  bacteria  of 
various  kinds.  It  is  usually  these  small  forms  of  life,  and 
not  the  organic  compounds,  that  render  water  unfit  for 
human  use. 

The  inorganic  materials  of  natural  waters  consist  mainly 
of  soluble  salts,  such  as  carbonates,  chlorides,  and  sul- 
phates. They  are  chiefly  compounds  of  calcium,  magne- 
sium, sodium,  potassium,  and  iron.  These  compounds  are 
dissolved  or  taken  into  suspension  as  the  waters  run  over 
the  ground,  percolate  through  the  soil,  or  make  their  way 
through  rocky  strata. 

The  nitrates  and  nitrites  found  in  natural  waters  owe 
their  formation  to  the  nitrifying  organisms  in  the  soil. 
Dissolved  oxygen  is  another  substance  in  natural  waters 
and  is  important  for  the  part  that  it  plays  in  their  purifi- 
cation. 

Although  simple  tests  are  available  for  the  detection 
of  the  various  contents  of  natural  waters,  accurate 
quantitative  determinations  and  their  interpretation  re- 
quire a  skilled  chemist. 

The  following  analysis  gives  some  idea  of  the  substances 
contained  in  natural  waters.  Although  the  number  of 
dissolved  substances  may  be  large,  such  waters  are  actually 
very  dilute  solutions,  so  dilute  in  fact,  that  the  amounts 
of  the  dissolved  substances  are  expressed  in  parts  per 
million  by  weight. 


WHOLESOME    WATER  169 

ANALYSIS  OF  CROTON  WATKR,  NEW  YORK  CITY 

Appearance .     .     .     Very  slightly  turbid 

Color Light  yellow  brown 

Odor  (heated  to  100°  F.) Slightly  marshy 

Chlorine 2.100  parts  per  million 

Equivalent  to  sodium  chloride 3.460  parts  per  million 

Phosphates 0.000  parts  per  million 

Nitrogen  in  nitrates 0.250  parts  per  million 

Nitrogen  in  nitrites 0.000  parts  per  million 

Free  ammonia 0.015  parts  per  million 

Albuminoid  ammonia 0.170  parts  per  million 

Hardness  equivalent  to  calcium   carbonate, 

before  boiling 37.500  parts  per  million 

Hardness  equivalent  to  calcium  carbonate, 

after  boiling 33.300  parts  per  million 

Organic  and  volatile  matter  (loss  on  ignition)   15.000  parts  per  million 

Mineral  matter 66.000  parts  per  million 

Total  solids 81.000  parts  per  million 

145.  Pure  and  Wholesome  Water.  — The  value  of  a  water 
intended  for  drinking  does  not  depend  upon  the  number, 
but  rather  upon  the  kind  of  substances  that  it  contains, 
and  upon  certain  physical  characteristics.     A  satisfactory 
water  should  be  colorless,  should  be  free  from  turbidity, 
objectionable  tastes  and  odors,  and  should  not  contain  any 
substances,  or  forms  of  life  dangerous  to  health.      More- 
over, its  temperature  should  fall  within  the  range  at  which 
water  is  palatable.     Such  a  water  will  be  wholesome  and 
pure  in  a  sanitary  sense,  although  not  necessarily  pure  ac- 
cording to  the  chemist's  idea.    -A  knowledge  of  the  req- 
uisites  for  wholesome   water  may  best  be  gained  by  a 
consideration  of  the  factors  upon  which  these  desirable 
qualities  depend. 

146.  Color  of  Water.  —  Ground  waters  are  usually  color- 
less, while  surface  waters  often  vary  from  light  yellow  to 


170  WATER 

dark  brown.  The  color  is  usually  due  to  organic  material, 
which  is  dissolved  as  the  water  drains  through  swampy  or 
forest  areas.  Occasionally  the  water  supply  of  a  city 
may  become  discolored  from  the  surface  washings  of  the 
reservoir  area  due  to  a  heavy  rain.  Many  colored  waters 
are  wholesome,  but  are  unattractive  and  therefore  un- 
desirable for  public  water  supplies.  In  the  reports  of 
sanitary  chemists,  the  color  of  water  means  color  due  to 
dissolved  substances  and  should  not  be  confused  with 
color  due  to  turbidity. 

147.  Turbidity.  —  The  turbidity  of  water  is  due  to  par- 
ticles of  suspended  matter  of  various  kinds,  sand  and  partic- 
ularly clay  being  the  most  frequent  materials.     A  water 
may  contain  a  considerable  amount  of  sand  and  still  look 
clean,  while  a  very  small  amount  of  clay  may  produce 
very  turbid  water.     The  latter  waters  owe  their  turbidity  to 
iron  compounds  changing  from  ferrous  to  ferric  salts.     At 
certain  seasons  of  the  year,  several  forms  of  plant  life 
(algae   and   diatoms)   grow  with   great  rapidity,   and  as 
rapidly  disintegrate,  clouding  the  water  with  dead  and 
dying  plant  tissues.     Organic  material  from  the  soil  often 
causes  waters  to  become  turbid,  especially  when  the  ma- 
terial is  in  an  active  state  of  decomposition.     The  iron 
bacterium,  which  thrives  in  the  presence  of  iron  compounds 
and    organic   matter,  makes   many  waters   turbid.     The 
turbidity  due  to  suspended  clay  or  sand,  although  un- 
desirable, is  far  less  likely  to  make  a  water  unwholesome 
than  a  turbidity  due  to  suspended  organic  matter  in  a 
state  of  decomposition. 

148.  Odor  and  Taste.  —  The   usual   agreeable   odor  and 
taste  of  water  is  due  mainly  to  dissolved  oxygen  and  car- 
bon dioxide.     Water  without  these  dissolved  gases  tastes 


TRANSMISSION  OF  DISEASE  BY   WATER       171 

flat.  Iron  or  sulphur  compounds,  and  certain  other  salts, 
give  some  waters  a  pronounced  odor  and  taste.  Some 
spring  waters  have  an  earthy  odor,  due  to  volatile  sub- 
stances absorbed  from  the  soil.  Occasionally  the  odor  and 
taste  are  due  to  putrefying  organic  material,  but  more 
frequently  are  due  to  oils  formed  in  the  cells  of  certain 
organisms.  A  diatom,  asterionella,  gives  an  aromatic 
odor.  The  blue-green  alga?  give  grassy  odors,  —  one  vari- 
ety, anabcena,  mixed  with  water  gives  it  a  taste  like  green 
corn.  Minute  and  lower  forms  of  animal  life  are  usually 
responsible  for  fishy  tastes  and  odors. 

149.  Transmission  of  Disease  by  Water.  —  The  disastrous 
effects  resulting  from  the  use  of  impure  water  were  clearly 
shown  in  the  southern  camps  of  our  soldiers  in  the  Spanish 
war  of  1898.  Neglect  of  sanitary  precautions  led  to  a 
greater  loss  of  life  and  health  than  that  due  to  the  military 
operations.  Six  years  later,  Japan,  profiting  by  the  ad- 
vance in  sanitary  science,  sent  its  chemists  and  sanitary 
engineers  ahead  of  the  main  army  to  test  the  water  sup- 
plies and  indicate  the  wholesome  ones.  When  the  army 
was  in  camp,  the  enforcements  of  strict  sanitary  regula- 
tions prevented  the  contamination  of  the  sources  of  water. 
As  a  result,  the  Japanese  army  was  free  to  a  marked  de- 
gree from  the  diseases  that  had  weakened  many  armies 
in  earlier  wars.  Too  often  the  value  of  pure  water  has 
been  demonstrated  to  towns  and  cities  by  disastrous  epi- 
demics due  unquestionably  to  polluted  water  supplies. 

The  transmission  of  disease  by  water  depends  upon  (1) 
the  introduction  of  the  disease  germs  into  the  water,  usu- 
ally by  sewage,  (2)  the  survival  and  maintenance  of  the  vi- 
tality of  the  germs  under  favorable  conditions  until  they  are 
taken  into  the  system.  Fortunately  the  conditions  pre- 
vailing in  natural  waters  result  in  the  death  of  most 


172 


WATER 


disease  germs.  Accordingly  the  number  of  water-borne 
diseases  is  not  large,  but,  on  the  other  hand,  they  are 
among  the  most  deadly,  as  they  give  rise  to  serious  affec- 
tions of  the  intestinal  tract.  Asiatic  cholera,  typhoid 
fever,  dysentery,  and  cholera  infantum  are  known  to  be 
transmitted  by  water.  In  fact,  severe  epidemics  of  these 
diseases  have  been  traced  to  the  use  of  contaminated  water. 


Courtesy  of  The  American  Museum  of  Natural  History. 

FIG.  65. — WATER-BORNE  BACTERIA. 

a,  Bacillus  of  typhoid  fever;   b,  Spirillum  of  Asiatic  cholera;    c,  Staph- 
ylococci.     (Magnified  4000  diameters.) 

The  cholera  epidemic  of  1892  in  Hamburg  and  Altona 
strikingly  demonstrated  that  the  spread  of  the  disease  was 
mainly  due  to  impure  river  water.  These  two  cities  are 
practically  one,  as  no  natural  boundary  separates  them. 
Hamburg  took  its  water  from  the  river  Elbe  and  did  not 
filter  it,  while  Altona,  with  water  from  the  same  river,  and 
still  more  contaminated,  used  an  efficient  system  of  sand 
filtration.  The  following  table  tells  its  own  story  : 


CITY 

POPULATION 

CASES  OF 
CHOLERA 

CHOLERA 
DEATHS 

DEATH  RATE 

PER  10,000 

Hamburg  . 
Altona  .     .     . 

600,000 
150,000 

17,000 
500 

8,600 
300 

134.0 
21.3 

PURIFICATION  OF   WATER  173 

One  block  in  Hamburg  which  happened  to  be  supplied 
with  Altona  water  was  free  from  the  disease,  while  the 
neighbors  across  the  street  paid  the  penalty  for  drinking 
the  impure  Hamburg  water.  No  doubt  many  of  the 
cholera  cases  of  Altona  were  contracted  by  the  Altona 
people  while  at  their  daily  work  in  Hamburg. 

The  following  table  shows  the  decrease  in  typhoid  in  this 
country  concurrent  with  the  increasing  number  of  filtered 
public  water  supplies.  The  statistics  are  for  twelve  states, 
all  the  New  England  States,  New  York,  New  Jersey,  Mary- 
land, Michigan,  Minnesota,  and  California. 

AVERAGE  TYPHOID  DEATH  RATE  PER  100,000 1 

1880 55 

1885 46 

1890 36 

1895     . 28 

1900 23 

1905 21 

1910 19 

Instance  after  instance  can  be  cited  to  show  that  the 
prevalence  of  water-transmitted  diseases  could  have  been 
much  restricted  by  the  use  of  pure  water.  Whatever  the 
source  of  the  supply  may  be.  care  must  be  taken  to  prevent 
the  contamination  of  the  water.  When  pollution  occurs, 
the  use  of  the  water  must  be  discontinued  till  proper  meas- 
ures have  been  taken  to  purify  it.  The  close  watching 
of  the  water  supplies  is  as  important  to  the  dweller  in  the 
country  as  it  is  to  the  city  inhabitant.  It  is  one  of  the 
most  important  factors  in  the  conservation  of  the  health 
of  the  people. 

150.  Purification  of  Water.  —  Boiling  is  the  best  household 
method  for  killing  disease-producing  bacteria.  In  typhoid 

iFrom  Whipple's  Value  of  Pure  Water,  John  Wiley  &  Sons. 


174  WATER 

epidemics,  the  first  regulation  should  be  to  boil  all  water 
used  for  drinking  or  in  the  preparation  of  food.  The  use 
of  boiled  water  for  babies  is  a  familiar  application  of  boil- 
ing as  a  means  of  purification.  There  are  a  number  of 
processes  for  the  purification  of  water  on  a  large  scale,  and 
in  most  cases  they  are  modifications  of  the  method  nature 
employs.  The  processes  may  be  roughly  classified  as 
mechanical,  chemical,  and  biological.  They  may  be  em- 
ployed separately  or  together. 


FIG.  66.  —  AERATION  OF  WATER. 

151.  Aeration.  —  Aeration  means  the  bringing  of  water 
in  contact  with  air,  so  as  to  increase  the  per  cent  of  dis- 
solved oxygen.  This  is  usually  done  by  spouting  the 
water  into  the  air  (Fig.  66),  or  by  allowing  it  to  flow  down 
over  a  steep  and  rocky  slope.  A  certain  amount  of  puri- 
fication is  accomplished  by  aeration,  but  alone  it  is  not 
to  be  relied  upon.  Aeration,  however,  is  very  valuable  in 
improving  the  taste,  smell,  and  appearance  of  water.  The 
process  often  gets  rid  of  unpleasant  dissolved  gases,  such 
as  hydrogen  sulphide.  Other  impurities  are  acted  upon  by 
the  dissolved  oxygen.  In  running  streams  the  percentage 


INTERMITTENT  SOIL   FILTRATION  175 

of  dissolved  oxygen  should  not  fall  below  50  %  of  the 
amount  required  for  saturation,  or  else  the  waters  will  be 
unable  to  rid  themselves  of  organic  impurities. 

152.  Light.  —  Sunlight  is  an  effective  destroyer  of  germs, 
but  its  value  is  limited  in  that  it  reaches  only  the  surface 
layers  of  water.     The  deeper  waters  of  a  reservoir  may 
be  unaffected.     Light  brings  about  the  growth  of  taste- 
producing  algse,  as  was  the  case  when  the  underground 
waters  taken  for  the  Brooklyn  supply  were  exposed  in 
the  Ridgewood  reservoir. 

It  is  better  to  store  ground  and  deep-seated  waters  in 
the  dark  ;  surface  waters  may  be  stored  either  in  open  or 
covered  reservoirs.  It  is  well  to  remember  that  water  is 
uninjured  by  storage  in  the  dark. 

153.  Cold.  —  It  has  been  found  that  the  critical  temper- 
ature for  bacteria  is  about  0°  C.     Germs  that  can  pass  be- 
low that  temperature  alive  have  been  found  to  stand  even 
such  temperatures  as  those  produced  by  liquid  air.     The 
length  of  exposure  to  a  freezing  temperature,  rather  than 
the  degree  of  coldness,  is  the  controlling  factor  in  the 
vitality   of  bacteria.     Less   than  5  %    of  the  bacteria  re- 
main alive  in  ice  formed  on  the  surface  of  deep  water. 
If  such  ice  is  stored  until  the  summer  months,  it  is  still 
safer  for  use.     It  is  never  safe,  however,  to  rely  upon  cold 
alone  for  the  purification  of  water.     Ice  taken  from  pol- 
luted water  is  unsafe  to  use. 

154.  Intermittent    Soil    Filtration.  —  Many    well    waters 
may  be  safe  to  use,  although  they  derive  part  of  their  sup- 
ply from  waters  which  have  been  polluted.     Such  waters 
are  filtered  as  they  pass  through  the  soil,  and  the  organic 
material  in  them  is  subjected  to  the  action  of  nitrifying 


176  WATER 

bacteria.  This  formation  of  soluble  nitrates  from  sewage 
and  other  waste  matter  not  only  requires  a  supply  of  oxy- 
gen from  the  air,  but  sufficient  time  must  be  allowed  for 
the  process.  Thus  the  capacity  of  the  soil  for  ridding 
polluted  water  of  its  impurities  is  limited.  A  steady  flow 
of  polluted  waters  cannot  be  taken  care  of.  The  greatest 
danger  arises  in  times  of  heavy  rains.  Highly  protective 
as  soil  nitration  often  is,  it  is  hazardous  to  depend  upon  it 
for  pure  water  from  a  polluted  source. 

155.  Mechanical  Processes  of  Purification.  —  The  mechan- 
ical processes  aim  to  remove  from  the  water  the  suspended 
matter,  including  some  of  the  bacteria.  Of  these  pro- 
cesses, sedimentation  and  filtration  are  the  chief  ones. 
They  are  doubly  interesting  as  adaptations  of  nature's 
processes  of  purifying  water. 

In  running  water,  the  coarser  sediment  usually  settles 
quickly,  but  the  finer  particles  of  clay  and  suspended  or- 
ganic matter  require  sufficient  time  for  settling.  For 
this  reason  sedimentation  is  carried  on  either  in  small  set- 
tling basins  or  in  storage  reservoirs.  The  water  is  allowed 
to  remain  quiet  until  the  suspended  matter  goes  to  the 
bottom.  In  the  settling  basin  the  treatment  requires 
from  a  few  hours  to  three  days,  depending  upon  the  nature 
and  amount  of  the  sediment.  When  the  water  is  collected 
in  large  reservoirs,  it  stands  for  a  much  longer  time,  and 
so  a  much  clearer  water  is  obtained. 

Experiments  have  shown  that  this  process  of  plain  sed- 
imentation removes  a  large  proportion  of  the  bacteria,  but 
that  it  is  essentially  a  preliminary  process  which  cannot 
be  relied  upon  to  remove  all  the  dangerous  bacteria,  par- 
ticularly in  water  polluted  with  sewage. 

In  many  plants  for  water  purification,  sedimentation  is 
followed  by  filtration  through  mechanical  filters  or  through 


MECHANICAL  PROCESSES   OF  PURIFICATION     177 


sand  filters.  A  mechanical  filter  (Fig.  67)  is  a  device  for 
passing  water  through  a  layer  of  sand  at  a  rapid  rate. 
When  the  sand  becomes  dirty,  it  is  washed  by  reversing 
the  current  of  water.  Mechanical  filters  are  used  in  con- 
nection with  coagulation,  and  owe  their  effectiveness  to 
their  straining  action  rather  than  to  sedimentation  in  their 
pores.  As  the  water  runs  through  at  a  rapid  rate,  the 
particles  in  the  water  must  be  large  enough  to  be  screened 
out  by  the  sand  and  not  so  numerous  as  to  clog  the  filter. 

Sand  filters  (Figs. 
68  and  69)  have  the 
water  run  through 
them  at  a  slower 
rate  than  mechani- 
cal filters.  Their 
effectiveness  is 
largely  due  to  a 
gelatinous  layer 
formed  on  the  sur- 
face of  sand  by  the 
organisms  in  the 
water.  Moreover, 
in  the  sand  filters, 
as  the  upper  layer 
of  sand  soon  becomes 

dirty  and  clogged,  it  is  periodically  scraped  off  and  washed. 
In  Fig.  70  is  shown  a  line  of  sand  bins  with  a  sand  washer 
in  the  foreground. 

Sand  filters  are  superior  to  mechanical  filters  in  sim- 
plicity of  construction,  in  providing  a  far  greater  filtra- 
tion area  for  the  same  cost,  and  in  giving  at  the  slower 
rate  a  more  thorough  straining  and  bacteriological  purifi- 
cation. In  many  cases,  sand  filters  are  used  for  waters 
for  which  a  rough,  inexpensive  process  suffices,  because 


FIG.  67. —  MECHANICAL  FILTER. 


178 


WATER 


FIG.  68.  —  SAND  FILTERS. 


1o 


and  Line 

j 
i 

> 

Sand  Line 

• 

Split  Tile  Corer 

Open  joints 

Wl;  1 

"V 

)                    \           Split  Tile  Drain 

'                       \                 / 

HP" 

T 

...,.--:.^i^W^^.A',:...^U.,.:.:Jr 

T 

;~...:.JU-....-.-4-*..-. 

FIG.  69.— SAND  FILTERS.     (SECTIONAL.) 


SEDIMENTATION    WITH   COAGULATION 


179 


they  are  not  turbid  enough  to  require  a  preliminary  treat- 
ment. 

156.  Sedimentation  with  Coagulation.  —  The  process  of 
plain  sedimentation  described  in  §  155  is  not  effective 
when  the  suspended  matter  is  in  a  finely  divided  state. 
In  such  cases,  sedimentation  is  aided  by  the  use  of  a  gelat- 
inous substance  produced  by  a  chemical  reaction.  The 
whole  process  is  known  as  a  sedimentation  with  coagu- 


FIG.  70.  —  EXTERIOR  OF  WATER  FILTRATION  PLANT. 

lation.     The   coagulant   employed   is   usually   aluminum 
hydroxide. 

When  lime  water  is  added  to  a  solution  of  aluminum 
sulphate,  a  white  gelatinous  precipitate  of  aluminum 
hydroxide  is  formed  :  • 


A12(SO4)3 

aluminum 
sulphate 


3  Ca(OH)2 

calcium 
hydroxide  • 


2  A1(OH)3  +  3  CaSO4 

aluminum  calcium 

hydroxide  sulphate 


When  this  reaction  occurs  in  water  containing  suspended 
matter,  the  particles  in  suspension  become  entangled  in 


180  WA  TER 

the  gelatinous  hydroxide.  This  coagulant  carries  down 
with  it  the  greater  part  of  the  sediment  and  the  disease 
germs  in  the  water.  When  the  coagulant  with  its  en- 
trapped impurities  is  removed  by  some  mechanical  device, 
the  water  is  left  comparatively  pure. 

Many  natural  waters  are  temporary  hard  waters,  in  that 
they  contain  in  solution  either  calcium,  magnesium,  or  fer- 
rous bicarbonates,  or  mixtures  of  these.  These  bicarbon- 
ates  themselves  react  with  aluminum  sulphate  to  form 
aluminum  hydroxide  without  the  use  of  lime  : 

A12(S04)3  +  3  CaH2(C03)2  — >- 

aluminum  calcium 

sulphate  bicarbonate 

2  A1(OH)3  +  3  CaSO4  +  6  CO2 

aluminum  calcium  carbon 

hydroxide  sulphate          dioxide 

In  water  purification  plants,  the  temporary  hardness  of 
the  water  is  determined,  and  then  a  calculated  amount  of 
aluminum  sulphate  is  added  so  as  to  react  with  all  the 
bicarbonate.  In  waters  requiring  both  the  aluminum  sul- 
phate and  the  calcium  hydroxide,  such  amounts  of  lime 
(CaO)  and  aluminum  sulphate  are  used  as  will  not  leave 
an  excess  of  either  after  the  reaction  has  taken  place.  The 
amounts  of  chemicals  required  per  million  gallons  of  water 
are  usually  astonishingly  small.  Even  the  calcium  sulphate 
formed  by  the  reaction,  which  remains  for  the  most  part 
in  the  water,  does  not  render  it  excessively  hard  or  unfit 
for  drinking. 

157.  Other  Chemical  Processes  of  Purification.  —  Chlorine 
and  ozone  are  two  substances  that  have  recently  come 
into  use  as  effective  in  purify  ing.  water.  In  the  chlorina- 
tion  processes  chlorine  is  produced  from  some  hypochlorite, 
as  sodium  hypochlorite  or  calcium  hypochlorite  (bleaching 


HARD    WATERS  181 

powder).  The  nascent  chlorine  generated  is  most  vigor- 
ous in  its  germicidal  action.  Jersey  City,  New  Jersey, 
has  a  successful  plant  of  this  type. 

In  the  ozone  processes,  the  ozone  is  produced  by  electric 
discharges  in  special  apparatus  known  as  ozonizers,  and  then 
is  allowed  to  bubble  up  through  long  cylinders  to  which 
water  is  admitted  at  the  top.  These  streams'of  extremely 
minute  bubbles  of  ozone  destroy  all  forms  of  bacterial  life. 
Ozone  is  preferable  to  chlorine,  as  an  excess  of  ozone  in 
the  water  is  not  objectionable,  while  even  a  slight  excess 
of  unused  chlorine  is  highly  undesirable.  In  St.  Peters- 
burg, the  much-polluted  waters  of  the  Neva  are  rendered 
safe  for  drinking  by  the  ozone  process.  Paris  has  recently 
installed  an  ozone  plant  which  purifies  most  successfully 
the  dirty  water  of  the  Seine.  Turbid  waters  always 
undergo  a  preliminary  treatment  before  being  chlorinated 
or  ozonized. 

158.  Hard  Waters.  — In  the  narrow  sense,  hard  waters 
are  those  which  contain  in  solution  salts  of  calcium  and 
magnesium,  particularly  their  carbonates  and  sulphates. 
The  term,  however,  has  been  extended  to  include  waters 
containing  iron  compounds  and  certain  other  soluble  salts. 
A  better  definition  of  hard  water  would  be  to  describe  it 
as  water  containing  mineral  substances  that  precipitate  or 
curdle  soap.  Water  containing  sodium  chloride  resembles 
hard  water  in  this  action,  because  the  salt  decreases  the 
solubility  of  the  soap. 

Water  that  contains  less  than  25  parts  of  such  dissolved 
substances  per  million  parts  of  water  is  not  .noticeably 
hard.  When  the  hardness  is  above  50  parts  per  million, 
the  water  is  classed  as  distinctly  hard  ;  above  100  parts  it 
will  be  known  as  very  hard.  In  some  cases  a  hardness  of 
200  or  300  parts  per  million  exists. 


182  WATER 

Hard  waters  are  of  two  kinds — permanent  and  tempo- 
rary. Waters  that  are  not  softened  by  boiling  in  an  open 
vessel  are  permanent  hard  waters  ;  temporary  hard  waters 
are  softened  by  such  boiling. 

159.  Temporary  Hard  Waters.  —  These  contain  in  solu- 
tion either  the  bicarbonate  of  calcium,  of  magnesium,  of 
ferrous  iron,  or  mixtures  of  these.  The  production  of 
such  a  hard  water  is  typified  by  the  natural  formation 
of  calcium  bicarbonate.  When  the  surface  waters  drain 
through  the  soil,  they  absorb  carbon  dioxide  formed  by 
the  decaying  of  organic  matter.  Carbonic  acid  is  formed 
in  the  water  : 

H20   +   C02— -^H2C03 

water  carbon  carbonic 

dioxide  acid 


FIG.  71. — SECTION  OF  CAVES  IN  LIMESTONE  REGION. 

When  the  water  containing  carbonic  acid  flows  over  lime- 
stone, the  calcium  carbonate,  of  which  it  is  mainly  com- 
posed, dissolves  (Fig.  71),  forming  calcium  bicarbonate,  a 
soluble  substance  : 

CaCO3  +  H2CO3  — *-  CaH2(CO3)2 

calcium  carbonic  calcium 

;.%.        carbonate  acid  bicarbonate 

When  this  temporary  hard  water  is  boiled,  the  following 
decomposition  occurs : 

CaH2(C03)2  — >-  CaC03  +   H2O   +   CO2 

calcium  calcium  water          carbon 

bicarbonate  carbonate  dioxide 


HARD    WATERS  AND   SOAP  183 

The  calcium  carbonate  precipitates  and  the  carbon  dioxide 
escapes  as  a  gas. 

Temporary  hard  water  containing  ferrous  bicarbonate, 
FeH2(CO3)2,  is  similarly  decomposed  by  boiling,  but  the 
decomposition  is  complicated  if  the  oxygen  of  the  air 
gains  access  to  the  precipitate.  The  total  action  may  be 
represented  by  the  equation  : 

4  FeH2(CO3)2  +  2  H2O  +  O2  —  >•  4  Fe(OH)8  +  8  CO2 

ferrous  water         oxygen  ferric  carbon 

bicarbonate  hydroxide  dioxide 

Ferric  hydroxide,  on  further  drying,  is  converted  into  a 
compound  resembling  iron  rust.  An  iron  hard  water 
undergoes  the  changes  just  mentioned  simply  on  standing 
in  contact  with  air. 

160.  Permanent  Hard  Waters.—  Gypsum,  CaSO4.2  H2O, 

is  one  of  the  most  widely  and  abundantly  distributed 
minerals.  On  this  account,  arid  because  of  its  solubility 
in  water,  most  permanent  hard  waters  contain  calcium 
sulphate,  CaSO4.  Magnesium  sulphate,  MgSO4,  is  also 
frequently  found  in  permanent  hard  waters. 

161.  Hard  Waters  and  Soap.  :  —  Soft  water,  or  water  free 
from  dissolved  mineral  salts,  readily  forms  lather  with  soap. 
When,  however,  soap  is  used  with  a  hard  water,  part  of 
the  soap  is  wasted  by  combining  chemically  with  the  dis- 
solved substances  in  the  water  to  form  an  insoluble  soap. 
The  reaction  in  the  case  of  calcium  sulphate  may  be  illus- 
trated by  the  equation  : 


2  NaC1?H860a  +  CaS04  —  *•  Ca(C18H3502)2  +  Na2SO4 

sodium  calcium  calcium  sodium 

stearate  (soap)  sulphate  stearate  sulphate 

The  calcium  stearate  is  a  white  curd-like  precipitate. 
Until  all  the  calcium  is  precipitated  out  of  the  hard  water, 
the  water  will  not  form  suds  freely. 


184  WATER 

The  soap-destroying  qualities  of  hard  water  is  a  decided 
factor  in  the  cost  of  soap  for  household  use.  It  has  been 
found  that  one  pound  of  average  soap  will  soften  about 
200  gallons  of  water  that  has  a  hardness  of  25  parts  per 
million.  An  increase  of  1  part  per  million  in  hardness 
means  an  increase  of  §10  in  the  cost  of  soap  to  soften  a 
million  gallons  of  water. 

Although  the  waste  of  soap  is  the  principal  disadvan- 
tage of  hard  waters  for  household  use,  it  is  not  the  only 
one.  The  precipitates  of  calcium  and  magnesium  stearates 
fill  the  pores  of  the  skin,  making  thorough  cleansing  diffi- 
cult. In  the  laundry  these  precipitates  get  between  the 
fibers  of  the  clothes,  giving  a  dingy  appearance  after 
washing.  Hard  waters  tend  to  encourage  the  use  of  soaps 
or  washing  powders  that  contain  considerable  free  alkali. 
Such  cleansing  agents  are  injurious  to  fabrics.  The  un- 
sightly scums  in  wash  basins  and  bath  tubs  are  mainly  due 
to  deposited  calcium  and  magnesium  soaps. 

162.  Boiler  Scale.  —  When  hard  waters  are  heated, 
a  deposit  or  scale  is  formed  on  the  inside  of  the  boiler, 

kettle,  or  pipe  (Fig.  72). 
In  time  this  becomes  of  suf- 
ficient thickness  to  retard 
greatly  heating  the  water. 
It  has  been  estimated  that 
a  layer  of  calcium  sulphate 
scale  offers  from  twenty  to 
fifty  times  as  much  resist- 

FIG.  72. — PIPE  FROM  WATER  BACK  IN  ,.  ,  ,. 

STOVE  SHOW.NO  SCALE.  ance    to    the    conduction    of 

heat  as  an  equal  thickness 

of  wrought  iron.  The  formation  of  such  scale  depends 
upon  change  in  solubility  due  to  an  increase  in  tempera- 
ture or  to  certain  chemical  reactions. 


DISADVANTAGES   OF  BOILER    SCALE  185 

When  a  temporary  hard  water  is  heated,  the  bicarbon- 
ates  are  decomposed : 

CaH2(CO3)2  — >-  CaCO3  +  H2O  +  CO2 

calcium  calcium  water         carbon 

bicarbonate  carbonate  dioxide 

The  calcium  carbonate  is  deposited  as  a  seft,  powdery 
scale  which  may  be  removed  by  "  blowing  off "  the  boiler. 
Magnesium  carbonate  is  similarly  deposited  from  the 
soluble  magnesium  bicarbonate.  On  further  heating  in 
the  boiler,  the  magnesium  carbonate  is  changed  into  mag- 
nesium hydroxide  which  settles  out : 

MgC03  +  H20  — >•  Mg(OH)2  +  C02 

magnesium        water  magnesium  carbon 

carbonate  hydroxide  dioxide 

The  calcium  sulphate  in  permanent  hard  waters  becomes 
almost  insoluble  when  the  water  under  pressure  in  the 
steam  boiler  reaches  a  temperature  of  120°  C.  (250°  F.). 
This  sulphate  forms  a  hard,  crystalline  scale,  which  is  so 
adherent  that  it  sometimes  has  to  be  chiseled  off  from  the 
inside  of  the  boiler.  Calcium  sulphate  while  depositing 
often  acts  as  a  binding  material  on  the  calcium  and  mag- 
nesium carbonates,  magnesium  hydroxide,  clay,  and  sand 
precipitated  or  suspended  in  boiler  waters.  In  this  man- 
ner scales  are  formed  which  are  difficult  to  remove. 

Another  source  of  boiler  scale  is  lubricating  oil  which 
gets  into  the  boiler  water.  The  floating  particles  become 
coated  with  a  scum,  and,  sinking  to  the  bottom,  form  an 
incrustation  which  is  an  exceedingly  poor  conductor  of 
heat. 

163.  Disadvantages  of  Boiler  Scale.  —  The  increase  in  the 
total  cost  of  coal  due  to  boiler  scale  is  a  serious  item  to 
steam  producers.  A  scale  \  inch  in  thickness  means  a 


186  WATER 

decided  loss  in  the  heating  efficiency  of  the  fuel.  More- 
over, the  boiler  shell  may  become  overheated  and  burnt 
(oxidized).  The  different  rates  of  expansion  of  boiler 
scale  and  iron  lead  to  strains  which  cause  leaks. 

164.  Corrosion  or  Pitting.  —  Hard  waters  lessen  the  life 
of  a  boiler  and  its  tubes  by  corrosion  or  pitting.     This 
may  be  due  in  part  to  carbon  dioxide  and  oxygen  dissolved 
in  the  water.     Salt  water  is  too  corrosive  to  be  used  in 
boilers.     Swampy  waters  may  be  very  corrosive  from  the 
presence   of  carbonic,    tannic,    humic,   and    other    acids. 
Water  from  mining  districts  often  contains  mineral  acids, 
particularly  sulphuric  acid,  from  the  oxidation   of   ores 
containing  sulphur. 

165.  Foaming.  —  Another  .serious  disadvantage  of  hard 
waters  is  the  foaming  they  may  cause  in  steam  boilers. 
Foaming  is  a  violent  frothy  ebullition  of  the  water  in  the 
boiler,   and  is  caused  by  an  excess  of  impurities.     The 
scale- forming  material  precipitates  as  a  fine  powder,  each 
particle  of  which  acts  as  a  point  of  steam  formation.     The 
excess  of  alkaline  salts  in  some  waters  makes  the  water 
foam  as  soon  as  it  is  heated  in  the  boiler.     The  best  way 
to  prevent  foaming  is  to  use  clean  water  in  a  clean  boiler. 

166.  Hard  Waters  in  Chemical  Industries.  —  Hard  waters 
are  unsuitable  for  use  in  dye  works.     The  dyes  do  not 
dissolve  well,  the  colors  are  frequently  altered,  and  the 
goods  may  be  unevenly  dyed,  even  to  the  extent  of  spot- 
ting.    In  the  tanning  of  leather,  a  hard  water  may  pre- 
vent the  proper  absorption  of  tannin,  resulting  in  brown 
stains  on  the  leather.     In  sugar  refining,  the  compounds 
that   give   water   its  hardness  may  be  absorbed  by  the 
animal  charcoal,  thus  lessening  the  power  of  this  sub- 
stance to  decolorize  or  bleach  the  sirup  filtered  through  it. 


SOFTENING   OF   WATER  187 

Waters  containing  iron  compounds  are  objectionable  in 
the  manufacture  of  pulp  and  paper,  as  brown  stains  are 
formed.  Even  an  ordinary  hard  water  may  interfere  with 
the  sizing  of  the  paper.  Only  within  a  few  years  have 
chemical  manufacturers  come  to  a  realization  of  the  value 
of  pure  water  in  their  operations. 


167.  Water-Softening.  —  The  recogniz^  disadvantages 
of  hard  waters  in  steam  production  ancKn  the  chemical 
industries  have  led  to  the  establishment  or  water-soften- 
ing plants.  The  operation  of  these  depend  upon  a  few 
chemical  reactions  in  which  lime  and  sodium  carbonate 
are  the  important  chemicals. 

When  limewater  is  added  to  a  calcium  temporary  hard 
water,  the  following  reaction  occurs  : 

CaH2(C03)2  +  Ca(OH)2  -^  2  CaCO3  +  2  H2O 

calcium  calcium  calcium  water 

bicarbonate  hydroxide  carbonate 

Magnesium  bicarbonate  is  similarly  decomposed  by  cal- 
cium hydroxide  : 


(c°3)2  +  Ca  (°H)2  —  *~  Mgc°3  +  CaCOg  +  2  H2O 

magnesium  calcium  magnesium      calcium  water. 

bicarbonate  hydroxide  carbonate      carbonate 

Since  magnesium  carbonate  is  more  soluble  than  calcium 
carbonate,  an  additional  quantity  of  lime  must  be  used  so 
as  to  form  insoluble  magnesium  hydroxide  : 

MgC03  +  Ca(OH)2  —  *-  Mg(OH)2  +  CaCO3 

magnesium          calcium  magnesium  calcium 

carbonate          hydroxide  hydroxide  carbonate 

Permanent  hard  waters  are  softened  by  the  use  of 
sodium  carbonate  in  its  cheaper  form  of  soda  ash  : 


188  WATER 

CaSO4  +  Na2CO3  —  ^  CaCO8  +  Na2SO4 

calcium          sodium  calcium          sodiuja 

sulphate       carbonate  carbonate        sulphate 

In  case  the  permanent  hard  water  contains  magnesium 
sulphate,  lime  is  used  in  addition  to  the  soda  : 

MgS04  +  Na2C03  +  Ca(OH)2  —  *- 

magnesium       sodium  calcium 

sulphate        carbonate        hydroxide 


magnesium  calcium  sodium 

hydroxide          carbonate        sulphate 

The  sodium  sulphate  formed  in  the  reaction  above  is  very 
soluble  and  not  particularly  harmful. 

Water  for  boilers  is  best  softened  before  it  is  fed  into 
the  boiler.  In  stationary  boiler  plants  this  is  often  partly 
accomplished  in  the  feed-water  heater,  which  utilizes  the 
heat  of  the  waste  steam  or  of  the  fuel  gases.  The  steam 
enters  at  the  bottom  of  the  heater  and  comes  in  contact 
with  wa^er  sprayed  in  or  splashed  against  plates.  The 
water  is  then  filtered  through  burlap  or  some  similar 
material  on  its  way  to  the  boiler. 

168.  Water-Softeners.  —  The  demand  for  water-softeners 
has  led  to  the  manufacture  of  numberless  boiler  compounds 
in  which  cheap  chemicals,  such  as  lime,  sodium  carbonate 
(soda  ash),  sodium  fluoride,  sodium  aluminate,  and  sodium 
phosphate,  have  been  put  up  and  sold  for  fancy  prices  to 
engineers.  Glutinous,  starchy,  ^and  oily  substances  are 
also  sold  for  water  softeners.  They  are  supposed  to 
surround  the  scale-forming  particles  mechanically  and 
prevent  their  cementing  into  a  scale.  These  substances 
are  not  particularly  effective,  as  they  thicken  and  foul  the 
water  more  than  they  prevent  the  formation  of  a  hard 
scale.  Kerosene  is  the  best  representative  of  a  class  of 


SUMMARY  189 

water-softeners  that  act  mechanically  and  also  loosen  the 
deposited  scale.     Boiler  graphites  are  also  widely  used. 

A  water-softener  for  boilers  should  precipitate  the  salts 
in  a  powdered  condition  so  that  they  may  easily  be  blown 
off.  Moreover  the  softener  should  contain  neither  acids 
nor  compounds  yielding  acids.  Engineers  in  most  cases 
can  rely  on  lime  and  soda  as  cheap  andjjj|eclive  remedies 
for  hard  water. 


169.  Softening  Plants.  —  Industrial  esWiisftments  re- 
quiring large  quantities  of  softened  water  usualty  find  it 
economical  to  install  water-softening  plants.  In  these  the 
initial  precipitations  are  carried  on  in  tanks  or  settling 
basins,  with  carefully  calculated  amounts  of  chemicals 
based  on  the  analysis  of  the  water.  After  the  settling,  the 
complete  removal  of  the  precipitate  is  accomplished  by 
some  form  of  rapid  filter,  as  cloth  filter  presses,  sand  filters, 
or  specially  devised  filters  of  metal. 


SUMMARY 

Natural  Waters  contain  gases  from  the  air,  inorganic  and  organic 
substances  from  the  soil,  and  lower  forms  of  plant  and  animal  life. 

The  Value  of  a  Drinking  Water  depends  upon  its  color,  taste, 
odor,  turbidity,  and  the  absence  of  impurities  harmful  to  the  body. 

Diseases  may  be  transmitted  by  water. 

Sterilization  of  Water  by  boiling  is  a  good  household  method. 
Natural  processes  of  purification  are  by  aeration,  light,  cold,  and 
intermittent  soil  filtration. 

Artificial  Methods  of  Water  Purification  are  generally  adaptations 
of  the  natural  processes.  Among  the  chemical  means  employed 
are  sedimentation  with  a  coagulant  like  aluminum  hydroxide, 
chlorination,  and  the  use  of  ozone. 


190  WATER 

Hard  Water  is  water  containing  mineral  substances  that  pre- 
cipitate or  curdle  soap.  They  waste  soap,  interfere  with  laundering, 
form  scale  in  boilers,  and  lessen  the  efficiency  of  many  industrial 
operations. 

Temporary  Hard  Waters  contain  in  solution  the  bicarbonate  of 
calcium,  of  magnesium,  of  ferrous  iron,  or  mixtures  of  these.  They 
may  be  softenecy^Jx>iling  or  by  the  addition  of  an  alkali. 


Permanent  •  ^Baters  usually  owe  their  hardness  to  calcium 
sulphate,  b^Pm?|Ssium  sulphate  and  other  dissolved  salts  are 
sometimes  found.  They  may  be  softened  with  sodium  carbonate. 


EXERCISES 

1.  What  are  the  advantages  of  pure  water  ? 

2.  Distinguish  between  surface  and  ground  waters. 

3.  M^kdoes  each  of  the  following  get  into  natural  waters : 
oxygen^^pon  dioxide,  ammonia,  nitrates  and  nitrites,  common 
salt,  sulphates,  and  bacteria  ? 

4.  State  the  desirable  characteristics  of  wholesome  drinking 
water. 

5.  To  what  do  natural    waters   owe   their   color?     Their 
turbidity  ? 

6.  Account  for  the  disagreeable  odors  and  tastes  of  some 
waters. 

7.  Why  does  freshly  distilled  water  taste  "flat"  ? 

8.  What  diseases  may  be  transmitted  by  water  ?     What 
epidemics  in  your  state  have  been  ascribed  to  impure  water  ? 

9.  When  and  why  should  water  for  drinking  and  cooking 
be  boiled  ? 

10.  How  does  aeration  purify  water? 

11.  What  effect  does  light  have  on  natural  waters  ? 

12.  Is  it  ever  safe  to  use  ice  taken  from  a  contaminated 
pond  or  river  ?     Explain. 


EXERCISES  191 

13.  What  are  the  limitations  to  the  purification  of  water  by 
intermittent  soil  filtration  ? 

14.  How  does  plain  sedimentation  purify  water  ? 

15.  Explain  the  use  of  a  sand  filter. 

16.  Explain,  with  the  aid  of  an  equation,  the  use  of  alumi- 
num hydroxide  as  a  coagulant. 

17.  Compare    the    chlorine    and    the    ozone- processes   of 
purification.  ^Hk 

18.  Define :    (a)    hard  water ;   (b)  teilH  •  hard   water ; 
(c)  permanent  hard  water.  ^^r^| 

19.  How  is  soap  wasted  by  hard  waters  ?   Equation?   What 
other  disadvantages  have  hard  waters  for  household  use  ? 

20.  Write  an  equation  to  show  the  softening  of  a  temporary 
hard  water  by  (a)  boiling,  (b)  the  addition  of  lime. 

21.  How  would  you  soften  a  permanent  hard  water  contain^ 
ing  calcium  sulphate  ? 

22.  What  is  boiler  scale?     Briefly  state  how  i  ;med. 
How  does  it  waste  coal  ? 

23.  What  are  "  boiler  compounds  "  ?     What  is  their  value  ? 


CHAPTER   XVIII 
TYPICAL  PROPERTIES  OP  METALS 

IN  addition^^^e  similarities  in  the  chemical  behavior 
of  metals  which  have  been  noted  in  the  chapters  on  Acids, 
Bases,  and  Salts,  there  are  certain  physical  characteristics 
typical  of  metals.  The  extent  to  which  each  metal 
possesses  these  various  properties  determines  its  use- 
fulness. 

170.  Conductivity.  —  All  metals  conduct  both  heat  and 
electricity.      When  a  silver  spoon  is  put  into  a  cup  of 
coffee,  theheat  of  the  liquid  is  conducted  to  the  end  of  the 
spoon.     When  the  poles  of  an  electric  battery  or  of  a 
dynamolflb  joined  with  a  copper  wire,  an  electric  current 
flows  through  the  wire.     The  best  conductor  of  both  heat 
and  electricity  is  silver,  while  copper  is  nearly  as  good. 
Gold  and  aluminum  rank  next  for  both  kinds  of  conduc- 
tion.    The  other  metals  rank  in  about  the  same  order  for 
heat  and  electrical  conductivity,  though  the  same  metal 
may  differ  in  the  percentage  of  its  heat  and  electrical  con- 
ductivity as  compared  to    copper.      Thus,  the  electrical 
conductivity  of  iron  is  about  l  that  of  copper,  while  its 
heat  conductivity  is  about  -J-.     In  general,  metals  rank 
higher   than    other   substances   in   conductivity    of   both 
kinds. 

171 .  Malleability. — It  is  characteristic  of  metals  that  they 
may  be  rolled  or  hammered  into  thin  sheets.     This  property 
is  malleability.      Gold  is  the    most  malleable   substance 
known  ;  that  is,  it  may  be  beaten  into  the  thinnest  sheets. 

192 


MALLEABILITY 


193 


Gold  leaf  -gorroo"  °^  an  ^nc^  thick  has  been  made.  Silver 
and  copper  can  be  rolled  and  hammered  into  thin  sheets 
and  foil.  Sheet  lead  was  formerly  extensively  used  as 
roofing  and  is  now  used  for  lining  acid  tanks.  Lead  foil 
is  used  to  line  chests  of  tea,  and  is  often  substituted  for 
tin  foil.  Wrought  iron  can  be  worked  into  a  great  variety 
of  forms  by  hammering  when  hot  (Fig.  73).  Sheet  iron  is 


* 


FIG.  73.  —  MALLEABILITY  OF  IRON. 

made  from  ingots  of  wrought  iron  by  rolling  between  hard- 
ened steel  rolls.  Hammering  or  rolling  tends  to  harden 
metals  and  make  them  more  brittle,  and  so  they  are  gen- 
erally "annealed"  or  softened  by  heating  to  redness  and 
then  cooling  slowly  several  times  during  the  sheet-making 
process.  Zinc  has  the  peculiar  property  of  being  brittle  at 
ordinary  temperatures,  but  is  malleable  between  100°  C. 
and  140°  C.  Sheet  zinc  rolled  between  these  tempera- 
tures retains  its  malleability  when  cooled  to  ordinary 
temperatures. 


194 


TYPICAL  PROPERTIES   OF  METALS 


/     ^ 


FIG.  74. 


172.  Ductility.  —  Some  metals  are  ductile,  that  is,  they 
can  be  drawn  into  wire.  In  making  wire,  the  metal  is  first 
rolled  into  a  rod  about  0.2  of  an  inch 
thick.  This  rod  is  thoroughly  soaked  in 
dilute  acid  to  remove  scale,  coated  with 
lime,  and  the  end  pointed.  The  pointed 
end  is  drawn  through  a  conical  hole  (Fig. 
A  7-C)  in  a  steel  drawplate,  the  hole  having 
a  diameter  Jjightiy  less  than  the  rod.  By  repeating 
the  process  with  smaller  and  smaller  holes,  wire  of  the 
desired  size  may  be  finally  produced  (Fig.  75).  During 
the  process  the  wire  is  kept  lubricated,  part  of  the  time 
with  flour  and  part  of  the  time  with  a  mixture  of 
grease  and  sulphuric  acid,  called  "  soap."  As  in  the  case 
of  rolling,  wire  drawing  hardens  the  metal  and  it  must  be 
frequently  annealed. 

The  fineness  of  the  smallest  size  wire  that  can  be  drawn 


FIG.  75.  —  LABORATORY  WIRE  DRAWING. 

from  a  metal  is  a  measure  of  its  ductility.    Platinum,  gold, 
silver,  and  iron  are  among  the  most  ductile  metals.    Plati- 


FUSIBILITY  195 

num  can  be  drawn  by  a  special  process  into  wires  less  than 
0.001  of  an  inch  in  diameter.  To  be  highly  ductile,  a 
metal  must  be  very  tenacious.  Steel  wire  is  made  that 
will  endure,  before  it  breaks,  a  pull  of  more  than  120  tons 
for  a  square  inch  of  cross  section  of  wire.  The  tensile 
strength  of  wire  per  square  inch  is  higher  than  that  of 
the  rods  from  which  it  was  drawn.  Wrought-iron  wire 
has  about  a  third  of  the  tensile  strength  of  the  best  steel 
wire,  but  is  much  more  flexible  and  is  cheaper  and  for 
these  reasons  is  much  used.  Copper  has  much  less  tensile 
strength,  but  is  very  ductile  and  its  electrical  conductivity 
is  very  important.  Recently  aluminum  wire  has  replaced 
copper  to  a  considerable  extent  for  transmission  lines,  as 
an  aluminum  wire  is  lighter  and  has  greater  tensile 
strength  than  a  copper  wire  which  will  carry  the  same 
electrical  current.  Lead,  tin,  and  zinc  cannot  be  drawn 
into  fine  wire.  Lead  fuse  wire  is  made  by  squeezing  lead 
through  a  die  by  means  of  a  hydrostatic  press.  Mallea- 
bility and  ductility  are  often  characteristic  of  the  same 
metal,  but  lead  and  tin  are  highly  malleable,  without  be- 
ing ductile. 

173.  Fusibility.  —  With  the  exception  of  mercury,  which 
is  a  liquid  at  all  temperatures  above  —  39°  C.,  the  common 
metals  have  high  melting  points.  The  more  refractory, 
such  as  platinum  and  tungsten,  require  a  temperature  of 
more  than  1700°  C.  to  melt  them.  Such  metals  are  com- 
monly melted  in  the  electric  arc  furnace.  Of  the  common 
metals,  iron  has  the  highest  melting  point,  arid  tin  the 
lowest.  Sodium  and  potassium  generate  enough  heat  in 
their  reaction  with  water,  to  keep  them  in  molten  drops 
on  the  surface  of  the  water  (§  22). 

The  wide  range  of  melting  points  in  the  alloys  will  be 
shown  in  the  discussion  of  that  subject.  The  following 


196 


TYPICAL  PROPERTIES   OF  METALS 


table  shows  the  more  important  metals  arranged  accord- 
ing to  their  melting  points  : 


METAL 

MPT.  °0. 

METAL 

MPT.  °C. 

METAL 

MPT.  °C. 

Mercury 
Tin 
Bismuth 

-39 
232 

270 

Zinc 
Aluminum 
Silver 

419 
657 
955 

Iron  (pig) 
Iron  (pure) 
Platinum 

1075 
1505 
1753 

Cadmium 
Lead 

322 
327 

Gold 
Copper 

1062 
1065 

Tungsten 
Tantalum 

2800 
2900 

174.  Hardness.  —  Hardness  may  in  general  be  denned 
as  resistance  to  change  of  shape  before  breaking.  Two 
substances  are  usually  compared  as  to  hardness  by  finding 
which  will  scratch  or  cut  the  other.  A  diamond  scratches 
glass ;  a  steel  knife  blade  scratches  lead.  We  say  that 
the  diamond  is  harder  than  glass,  the  steel  harder  than 
the  lead.  Tool  steel  is  harder  than  machine  steel.  But 
aTiardened  steel  tool  which  will  cut  machine  steel  easily 
will  scarcely  scratch  some  cast-iron.  Tempering,  the 
sudden  cooling  of  a  metal  from  a  red  or  a  white  heat, 
often  increases  the  hardness,  notably  in  the  case  of  steel. 
The  outer  layer  of  cast-iron  is  much  harder  than  the 
interior. 

All  the  common  metals  are  .hard,  as  compared  to 
wood.  Among  the  hardest  metals  are  tempered  steel, 
nickel,  and  iron.  Brass,  an  alloy  of  copper  and  zinc,  is 
harder  than  copper,  but  softer  than  iron.  Zinc  is  softer 
than  copper,  and  lead  can  readily  be  cut  with  a  knife. 
Some  of  the  less  familiar  metals,  such  as  sodium  and 
potassium,  can  be  cut  almost  as  readily  as  cheese.  No 
comparative  table  of  hardness  is  given  here,  as  the  metals 
rank  differently  according  to  the  form  in  which  they  are 


PHYSICAL   CONSTITUTION  OF  ALLOYS          197 

prepared  and  also  according  to  the  kind  of  test  for  hard- 
ness that  is  made. 

ALLOYS 

175.  Physical  Constitution  of  Alloys.  —  Alloys  are  usually 
made  by  melting  together  two  or  more  metals  to  form  a 
metallic  substance  of  practically  uniform  composition,  hav- 
ing definite  properties  of  its  own.  In  the  case  of  amal- 
gams, which  are  alloys  of  mercury,  melting  is  not  always 
necessary,  as  the  other  metal  or  metals  dissolve  in  the 
mercury.  It  is  very  convenient  to  think  of  the  alloys  as 
solutions  of  one  solid  metal  in  another  solid  metal,  and  so 
the  term  solid  solutions  is  often  applied  to  them.  In  most 
alloys,  the  metals  do  not  appear  to  form  compounds,  al- 
though there  are  a  few  cases  in  which  an  alloy  may  con- 
sist of  a  compound  of  two  metals  dissolved  in  an  excess  of 
one  of  them.  Like  solutions,  alloys  have  their  constitu- 
ents intimately  mixed  and  quite  uniformly  distributed 
throughout  the  mass.  The  microscope,  however,  usually 
shows  that,  except  in  the  case  of  the  metallic  compounds 
mentioned  above,  the  distribution  is  not  uniform,  but  that 
the  different  constituents  can  often  be  distinguished  in  the 
form  of  plates  or  crystals.  This  is  not  unlike  the  result 
obtained  from  the  freezing  of  a  solution  of  salt  and  water, 
in  which  the  crystals  of  salt  and  crystals  of  ice  lie  side  by 
side  and  can  be  distinguished  by  magnifying  the  salt  ice 
obtained. 

Some  metals  alloy  in  all  proportions,  just  as  alcohol  and 
water  dissolve  each  other  in  all  proportions.  In  other 
cases,  one  metal  will  alloy  with  another  only  up  to  a  cer- 
tain fixed  ratio.  When  one  metal  dissolves  in  another, 
the  melting  point  is  usually  lowered  just  as  the  freezing 
point  of  a  solution  is  lower  than  that  of  the  solvent. 
There  is  one  particular  alloy  of  two  metals  that  is  more 


198  TYPICAL   PROPERTIES   OF  METALS 

fusible  than  any  other  alloy  of  the  same  two  metals,  but 
the  proportions  in  this  more  fusible  alloy  are  not  those  of 
their  atomic  weights.  So  in  the  great  majority  of  cases, 
at  least,  the  alloys  are  mixtures  or  solid  solutions,  and  not 
chemical  compounds. 

176.  Fusible  Metals.  —  An  alloy  often  shows  physical 
properties  which  are  intermediate  between  those  of  the 
metals  composing  it.  Sometimes,  however,  its  hardness, 
or  fusibility,  or  ductility  may  greatly  exceed  the  corre- 
sponding property  of  any  of  the  metals  contained  in  the 
alloy.  Sodium  and  potassium,  with  individual  melting 

points  of  97°  and  62°,  respec- 
tively, form  an  alloy  which  is 
liquid  at  ordinary  tempera- 
tures. Solder  is  an  alloy  of 
lead  and  tin  in  various  propor- 
tions, according  to  the  melt- 
FIG.  76.  —  SAFETY  PLUG.  ing  point  desired  ;  "  half  and 

half,"  which  consists  of  equal 

parts  of  the  two  metals,  has  a  melting  point  of  188° 
C.,  which  is  less  than  that  of  either  metal.  Harder  or 
less  fusible  solders  have  a  larger  proportion  of  lead,  and 
soft  or  easy  solder  has  a  large  proportion  of  tin.  A  very 
fusible  solder  can  be  made  from  equal  parts  of  lead,  tin, 
and  bismuth ;  this  melts  at  121°  C. 

Fusible  alloys,  consisting  wholly  or  largely  of  lead,  tin, 
and  bismuth,  are  used  in  the  plugs  of  automatic  sprinkler 
systems,  and  in  safety  plugs  for  steam  .boilers  (Fig.  76). 
Most  of  the  steam  boiler  plugs  contain  zinc  instead  of  tin. 
As  long  as  the  plug  (F)  is  covered  with  water,  its  temper- 
ature remains  that  of  the  surrounding  water  (W).  When 
it  becomes  uncovered,  it  reaches  the  temperature  of  the 
heated  shell  of  the  boiler  (B)  and  so  melts,  allowing  steam 


AMALGAMS  199 

to  escape  and  giving  warning  of  low  water.  Wood's  alloy, 
often  used  in  sprinkler  systems,  contains  lead,  tin,  bismuth, 
and  cadmium  and  melts  at  60°  C.  (140°  F.).  A  fire  in  a 
room  provided  with  sprinklers  plugged  with  this  or  a  sim- 
ilar alloy,  would  soon  melt  the  plugs,  permitting  the  water 
to  gush  out  and  extinguish  the  fire. 

177.  Bearing  Metals.  —  It  is  highly  desirable   that   the 
bearings  in  which  the  axles  of  machinery  run  should  be 
lined  with  a  metal  which  shall  be  softer  than  the  axle,  and 
so  wear  away  faster.     It  should  also  be  fusible,  so  as  to 
melt  and  run  out  if  the  bearing  becomes  overheated.     Bab- 
bitt metal  is  the  best  known  of  these  bearing  alloys.     Tin, 
lead,  and  antimony,  or  tin  and  zinc  are  the  chief  constitu- 
ents of  commercial  Babbitt.    The  original  Babbitt  consisted 
of  3-7  parts  copper,  88-89  parts  tin,  and  7-4  parts  anti- 
mony.    The  metal  in  brass  bearings  is  from  65  %  to  92  % 
copper,  the  remainder  being  usually  tin  and  lead.     All  of 
these  bearing  metals  produce  less  friction   with  a  steel 
shaft  than  would  be  caused  by  a  steel  or  iron  bearing. 

178.  Amalgams.  —  These  have  already  been  defined  as 
alloys  of  mercury  with  other  metals.     They  are  soft  when 
first  formed,  but  soon  harden  into  a  crystalline  mass.     The 
silver  amalgam  used  by  dentists  for  filling  teeth  is  typical. 
The  powdered  silver  and  other  metals  are  mixed  with  the 
mercury  and  the  excess  of  the  latter  squeezed  out.     When 
forced  firmly  into  the  cavity,  the  amalgam  takes  a  hard, 
crystalline  form  in  a  few  hours.     Zinc  used  in  voltaic  cells 
is  usually  amalgamated  by  cleaning  with  acid  and  then 
rubbing  mercury  on  the  surface  of  the  zinc.     In  this  way 
a  surface  of  pure  zinc  is  constantly  presented  to  the  acid 
for  action,  and  the  zinc  lasts  longer. 

The  tendency  of  gold  and  silver  to  amalgamate  with 


200  TYPICAL  PROPERTIES   OF  METALS 

mercury  is  utilized  in  separating  these  metals  from  the 
quartz,  or  other  rock  material,  which  is  found  associated 
with  them  in  the  earth.  The  finely  ground  mixture  of 
metal  and  rock  is  carried  by  a  thin  stream  of  water  over 
the  surface  of  tables  coated  with  mercury.  The  precious 
metal  amalgamates  with  the  mercury  and  the  rock  material 
is  carried  off  by  the  water.  The  mercury  is  separated  by 
distillation  from  the  amalgam,  leaving  the  precious  metal 
ready  for  refining.  An  amalgam  of  tin  and  mercury  was 
formerly  used  on  the  back  of  mirrors,  but  its  place  has 
been  taken  by  a  film  of  pure  silver,  formed  by  the  reduc- 
tion of  silver  nitrate  with  which  the  glass  has  been  coated. 

179.  Brass  and  Bronze.  —  The  essential  constituents  of 
brass  are  copper  and  zinc,  in  varying  proportions,,  accord- 
ing to  the  use  to  which  it  is  to  be  put.  There  is  usually 
about  twice  as  much  copper  as  zinc,  and  small  percentages 
of  lead  and  tin  are  often  present.  When  a  red  brass  is 
desired,  as  for  buttons  to  be  gold  plated,  the  percentage 
of  copper  may  run  as  high  as  80%  or  even  90%.  Brass 
used  for  electrical  purposes  has  a  high  percentage  of  cop- 
per, to  increase  its  conductivity.  Brass  is  highly  malleable 
and  ductile. 

The  name  bronze  is  applied  to  a  great  number  of  alloys, 
which  are  essentially  copper  and  tin,  although  a  small  per- 
centage of  zinc  and  sometimes  of  other  metals  is  often 
present.  The  percentage  of  copper  in  bronze  is  higher 
than  is  that  in  ordinary  brass,  being  from  80%  to  90%. 
Bronze  for  statuary  contains  both  lead  and  zinc,  with  a 
reduction  in  the  proportion  of  tin.  Bell  metal  is  a  bronze 
with  a  large  proportion  of  tin.  Phosphor  bronze  contains 
from  0.2%  to  4%  of  phosphorus  in  the  form  of  phosphide 
of  copper  or  phosphide  of  tin.  It  is  very  hard  and  tena- 
cious and  is  not  corroded  by  water.  These  properties 


LIGHT  ALLOYS  201 

make  it  valuable  for  water  wheels  and  propellers,  as  well 
as  for  other  uses  demanding  a  metal  not  readily  altered  by 
wear  or  moisture. 

180.  German  Silver.  —  This  alloy  is  a  white  metal  con- 
taining from  18  %  to  30  %  nickel  alloyed  with  copper  and 
zinc,  3  or  4  parts  of  copper  being  used  to  1  of  zinc.     It  is 
hard,  takes  a  high  polish,  and  is  not  easily  corroded.     The 
electrical  resistance  of  German  silver  is  from  18  to  28 
times  as  great  as  that  of  copper,  and  it  is  largely  employed 
as  resistance  wire  in  electrical  work.     It  is  also  used  for 
making 'small  articles  and  is  the  "white  metal "  used  for 
the  interior  of  plated  ware. 

181.  Type  Metal. — Lead  and  antimony   are   here   the 
important  metals  and  from  10  %  to  20  %  of  -tin  is  added 
to  increase  the  fusibility.     The  antimony  gives  hardness 
to  the  softer  lead  and  tin.     It  also  causes  the  alloy  to 
expand  when  it  solidifies,  thus  filling  all  the  outlines  of 
the  mold  or  matrix,  and  so  making  a  clean-cut  impres- 
sion.    Books  are  not  printed  from  type,  as  type  metal 
is  not  hard  enough  to  stand  the  wear  involved  in  printing 
large    editions   without   becoming   dull,    so   copper-faced 
electrotype  plates  made  from  the  type  are  used  instead 
(see  §  415).     These  plates  can  be   preserved   for   future 
editions,  and  the  type  used  again  to  prepare  other  plates. 

182.  Light  Alloys.  —  For  many  purposes,  such  as  auto- 
mobile and  aeroplane  parts,  lightness  combined  with  tensile 
strength  is  the  most  important  feature  of  an  alloy.     For 
such  alloys  aluminum  is  used  as  a  base,  and  the  tensile 
strength  and  uniformity  of  the  castings  is  increased  by 
the   addition   of   other   metals.     Aluminum  bronzes   con- 
sist of  aluminum  alloyed  with  copper  and  zinc,  or  copper 
and   nickel.     They   combine   lightness,  hardness,    and   a 


202  TYPICAL   PROPERTIES   OF  METALS 

tensile  strength  from  once  to  twice  that  of  cast  iron. 
Magnalium  and  other  aluminum-magnesium  alloys  contain 
from  2%  to  10  %  of  magnesium,  alloyed  with  aluminum. 
This  does  not  increase  the  weight  of  the  alloy,  but  gives 
it  a  tensile  strength  nearly  that  of  machine  steel.  The 
future  use  of  aluminum  for  machine  parts  will  depend 
upon  the  perfecting  of  its  alloys. 

183.  Coins.  —  Our  gold  and  silver  coins  contain  10  % 
copper,  which  increases  their  hardness  and  so  causes  them 
to  wear  longer.  English  gold  pieces  contain  8.33  %  cop- 
per, and  English  silver  money,  7.5  %  copper.  Sterling 
silver  has  the  same  composition  as  English  silver  coins. 
Our  nickel  five-cent  pieces  are  75  %  copper  and  25  % 
nickel,  while  pennies  contain  3  %  of  tin  and  2  %  of  zinc 
with  95  °/o  copper. 

The  proportion  of  alloy  metal  used  with  gold  for  pur- 
poses other  than  coinage  is  not  usually  given  in  per  cent, 
but  in  "  carats."  Pure  gold  is  24  carats  fine ;  18-carat 
gold  is  |-|  gold  and  -£-%  copper  or  silver.  This  carat  is  not 
to  be  confused  with  the  carat  used  as  a  weight  for  pre- 
cious stones,  which  is  equal  to  200  milligrams. 

SUMMARY 

Metals  are  good  conductors  of  both  heat  and  electricity.  Silver, 
copper,  gold,  and  aluminum  are  the  best  conductors. 

Most  metals  can  be  rolled  or  hammered  into  thin  sheets.  Gold, 
silver,  tin,  aluminum,  and  copper  are  very  malleable. 

Some  metals  can  be  drawn  into  wire  by  passing  them  through  a 
tapering  hole  in  a  steel  plate.  Platinum,  gold,  silver,  copper,  and 
iron  are  especially  ductile. 

Both  rolling  and  wire  drawing  harden  metals,  so  they  must  be 
annealed  to  keep  them  from  becoming  brittle. 


EXERCISES 


203 


The  common  metals,  except  mercury,  have  high  melting  points. 

Metals  show  various  degrees  of  hardness.  Tempering  increases 
and  annealing  diminishes  hardness. 

Alloys  are  solid  solutions  of  two  or  more  metals.  They  are  not 
usually  chemical  compounds.  The  physical  properties  of  alloys  are 
not  always  intermediate  between  the  properties  of  the,  metals  com- 
posing them.  Many  alloys  have  a  lower  melting  point  than  any  of 
their  constituents,  e.g.  solder  and  fusible  alloys. 


IMPORTANT  ALLOYS 


NAME 


CONSTITUENTS 


Aluminum  bronze 

Amalgams     .     . 

Bearing  metal    . 

Brass   .... 

Bronze 

Coins    .... 

Fusible  metal 
German  silver    . 
Magnalium    . 
Solder  .... 
Type  metal    .     . 


Aluminum,  copper  and  zinc  or  nickel 

Mercury  with  other  metals 

Copper,  tin,  lead,  antimony 

Copper  and  zinc 

A  brass  with  tin,  and  sometimes  with  other  metals 

Gold  and  copper ;    silver  and  copper ;    copper  and 

nickel;  copper,  tin,  and  zinc 
Lead,  bismuth,  and  tin  or  zinc 
Nickel,  copper,  and  zinc 
Aluminum  and  magnesium 
Lead  and  tin 
Lead,  antimony,  and  tin 


EXERCISES 

1.  Why  is  copper  often  used  for  wash  boilers  ? 

2.  Which  is  better,  an  iron  teakettle  or  an  aluminum  tea- 
kettle?    Why? 

3.  Name  three  metals  or  alloys  used  as  electric  conductors. 
Which  is  the  best  conductor  ?     Why  are  the  other  materials 
used? 


4.   Name  four  kinds  of  foil  and  give  a  use  of  each. 


204  TYPICAL  PROPERTIES   OF  METALS 

5.  Why  is  lead  wire  manufactured  by  a  different  process 
from  copper  wire  ?     Describe  the  process  in  each  case. 

6.  Why  is  it  harder  to  keep  the  solder  fluid  when  solder- 
ing copper  than  when  soldering  tinware  ? 

7.  Why  may  an  empty  tin  pan  be  ruined  by  placing  it  on  a 
red-hot  stove  ? 

8.  Why   could  not   a  mercury  thermometer   be  used    by 
Arctic  explorers  ? 

9.  Arrange  five  common  metals  in  the  order  of  their  hard- 
ness.    If  you  were-  in  doubt  as  to  the  relative  hardness  of  two 
metals,  how  would  you  determine  it  experimentally  ? 

10.  What  is  an  alloy  ?     A  solid  solution  ?     Why  are  the 
alloys  not  regarded  as  chemical  compounds  ? 

11.  Explain  the  working  of  an  automatic  sprinkler  system. 

12.  Why  can  a  piece  of  tinware  be  soldered  without  melt- 
ing the  tin  coating  off  the  iron  ? 

13.  In  soldering  an  additional   part  to  an  article  already 
soldered,  would  you  use  hard  or  soft  solder  ?     Why  ? 

14.  What  is  Babbitt  metal?     Why  are  machine  bearings 
always  lined  with  this  or  some  similar  material  ? 

15.  Explain  the  production  and  use  of  gold,  silver,  and  zinc 
amalgams. 

16.  Give  the  composition  and  uses  of  each  of  the  following : 
brass ;  bronze ;  phosphor  bronze  ;  aluminum  bronze. 

17.  Give   the   composition   of  a  ten-dollar   gold   piece,   a 
quarter,  a  nickel,  a  penny. 

18.  Which  is  more  valuable,  a  sterling  silver  spoon  or  a 
spoon  of  the  same  size  made  of  coin  silver  ? 

19.  Give  the  percentage  composition  of  10-carat,  14-carat, 
and  18-carat  gold  rings. 


CHAPTER   XIX 

CARBON  COMPOUNDS 

• 

HYDROCARBONS,    SUBSTITUTION  PRODUCTS,  AND  ALCOHOLS 

184.  Nature  of  Organic  Compounds.  —  The  beginner  in 
chemistry  soon  becomes  familiar  with  a  few  carbon  com- 
pounds, such  as  carbon  monoxide,  carbon  dioxide,  and  the 
carbonates  of  sodium,  potassium,  ammonium,  and  calcium. 
These  compounds  are  not  very  different  from  the  similar 
compounds  of  other  elements.  The  majority  of  elements 
form  comparatively  few  compounds  and  these  are  simple 
in  structure.  Carbon,  however,  forms  numerous  com^ 
pounds,  complex  in  structure,  and  widely  varying  in  prop- 
erties. In  fact,  the  chemistry  of  carbon  compounds  is  so 
wide  a  domain  that  most  students  of  chemical  science 
merely  touch  upon  its  borders.  This  division  of  the  sub- 
ject is  often  termed  Organic  Chemistry,  an  old  name  that 
was  given  when  it  was  believed  that  the  complex  carbon 
compounds  could  be  produced  only  in  the  living  tissues  of 
plants  and  animals.  Years  of  patient  investigation,  how- 
ever, have  made  it  possible  to  produce  in  the  laboratory 
many  of  the  compounds  found  in  the  living  world,  as  well 
as  hundreds  of  others  that  have  not  yet  been  found  in 
nature. 

The  remarkable  power  of  carbon  to  form  compounds  is 
due  to  two  things  —  its  high  valence  (combining  power) 
of  four,  and  the  ability  of  the  carbon  atoms  to  unite  with 
each  other.  These  facts  are  well  illustrated  by  the  "hydro- 
carbons, a  class  of  carbons  containing  only  the  two  elements 
hydrogen  and  carbon.  To  imagine  the  arrangement  of  the 

205 


206 


CARBON  COMPOUNDS 


atoms  in  the  hydrocarbons,  it  is  convenient  to  use  graphic 
formulas.  In  these,  each  unit  of  valence  is  represented  by 
a  short  straight  line. 

Thus,  hydrogen  chloride  may  be  shown  H  —  Cl.  The 
short  straight  line  shows  a  valence  of  one  for  each  of  the 
combining  elements,  hydrogen  and  chlorine.  A  graphic 
formula  for  water  is  H  —  O  —  H.  This  shows  the  valence 
of  the  oxygen  atom  as  two.  We  represent  hydrogen  per- 
oxide H — O — O — H  and  sulphuric  acid  i/^NCr 

The   simplest    hydrocarbon    is    marsh   gas    or    methane, 
H 

I 
H — C — H.     This  hydrocarbon  is  the  lowest  member  of 

I 

H 

the  paraffin  series  of  hydrocarbons,  CH4,  C2H6,  C3H8, 
C4H10,  C5H12,  etc.  It  will  be  noticed  that  the  general 
formula  for  the  series  is  CnH2n  +  2,  where  n  represents  the 
number  of  carbon  atoms.  The  difference  between  two 
successive  members  of  the  series  is  CH2. 

HYDROCARBONS  OF  THE  METHANE  SERIES 


NAME 

FORMULA 

MOLEC- 
ULAR 
WEIGHT 

BOILING 
POINT 

FREEZING  (OR  MELT- 
ING) POINT 

Methane 

CH4 

16 

160°  C. 

Ethane 
Propane 
Butane 

C4Hio 

30 
44 

58 

-93 
-45 

+  1 



Ordinarily 
gaseous 

Isobutane 

C4Hio 

58 

-  11 



Pentane 
Decane 

CioH22 

72 
142 

36 
173 

-32° 

Liquid 

Hexadecane 

C16H34 

226 

287 

+  18 

Solid 

Octodecane 

CA 

254 

317 

28  j 

PARAFFIN  SERIES  207 

Two  substances  having  the  formula  C4H10  —  butane 
and  isobutane  —  are  known.  Graphic  formulas  show  why 
this  is  possible. 

H     H    H    H  H        H        H 

H— C— C— C— C— H  H— C  -  -  C  -  -  C— H 

H    H    H    H  H         I         H 

TT f* IT 

butane 


isobutane 

With  the  valence  of  carbon,  four,  and  of  hydrogen,  one, 
there  is  only  one  arrangement  of  the  atoms  possible  for 
methane,  ethane,  and  propane.  For  butane  two  may  be 
seen.  Moreover,  butane  and  isobutane  differ  in  their 
properties  (see  table).  For  pentane,  there  are  three  dif- 
ferent arrangements  of  the  atoms  possible.  The  more 
numerous  the  carbon  atoms,  the  greater  the  possibilities  in 
arrangement.  Thus  for  the  formula  C13H28,  802  different 
hydrocarbons  are  possible.  When  it  is  realized  that  some 
of  the  hydrogen  atoms  are  replaceable  by  radicals  such  as 
_OH,  — Cl,  — Br,  — SO4,  — NO3,  etc.,  a  still  further 
multiplication  of  the  number  of  possible  arrangements  be- 
comes evident.  Hence  the  arrangement  of  atoms  in  the 
molecule  is  still  another  factor  in  accounting  for  the  almost 
numberless  carbon  compounds.  The  graphic  formulas  are 
simply  convenient  means  of  representing  the  relations  and 
probable  arrangements  of  the  atoms  in  the  molecule. 

185.  Paraffin  Series.  —  Methane,  CH4,  is  the  simplest 
member  of  the  paraffin  series  of  hydrocarbons.  It  is  the 
chief  constituent  of  natural  gas.  Paraffin  is  derived  from 
two  Latin  words,  meaning  "  small  affinity,"  thus  charac- 


208  CARBON  COMPOUNDS 

terizing  the  chemical  inertness  of  these  hydrocarbons. 
They  are  inactive  with  concentrated  nitric  and  sulphuric 
acids,  and  resist  the  action  of  alkalies  and  most  oxidizing 
agents.  Paraffin  is  also  the  name  for  a  white  wax  of 
common  household  and  industrial  use.  It  contains  several 
of  the  higher  members  of  the  paraffin  series.  Petroleum 
(§  360)  consists  of  a  mixture  of  various  members  of  the 
paraffin  series. 

186.  Methane,  CH4,  is  the  simplest,  but  most  important 
member  of  the  paraffin  series.  It  is  the  only  hydrocarbon 
containing  but  one  carbon  atom. 

This  gas  is  formed  by  the  decomposition  of  many  organic 
compounds.  As  this  action  takes  place  in  vegetable  mat- 
ter immersed  in  the  stagnant  water  of  marshes,  methane  is 
known  as  marsh  gas.  The  bubbles  which  rise  to  the  sur- 
face when  such  stagnant  waters  are  stirred,  consist  mostly 
of  marsh  gas,  but  also  contain  some  carbon  dioxide  and 
nitrogen. 

In  coal  mines,  methane  is  known  as  fire  damp,  because  of 
its  inflammable  properties  when  mixed  with  air.  Natural 
gas  contains  over  90  %  of  methane. 

The  usual  laboratory  method  of  making  methane  is  by  a 
dry  distillation  of  a  mixture  of  soda  lime  and  sodium 
acetate: 

NaC2H3O2  +  NaOH  — *-  CH4  +  Na2CO3 

sodium  sodium  methane         sodium 

acetate  hydroxide  carbonate 

Soda  lime  is  a  mixture  of  quicklime  and  caustic  soda. 

Methane  is  a  colorless,  odorless  gas,  a  little  more  than 
half  as  heavy  as  air.  It  is  slightly  soluble  in  water.  Like 
the  other  members  of  the  paraffin  series,  it  is  a  very  stable 
compound,  resisting  the  action  of  the  strong  acids  and 
alkalies  and  even  that  of  oxidizing  agents.  The  action  of 


ETHYLENE   SERIES  209 

methane  with  the  halogens  will  be  treated  in  §  190.  The 
kindling  temperature  of  methane  is  higher  than  that  of 
hydrogen  and  its  high  heat  of  combustion  makes  it  a  valu- 
able constituent  of  fuel  gases.  The  equation  for  the  com- 
plete combustion  of  methane  is: 

CH4  +  2O2  -^-  CO2  +  2H2O^ 

methane    oxygen  carbon          water 

dioxide 

187.  TJnsaturated  Hydrocarbons.  —  In  the  paraffin  hydro- 
carbons, we  saw  that  the  carbon  atoms  were  joined  by 
single  bonds.  There  are  other  series,  however,  whose 
formation  depends  upon  the  fact  that  adjacent  carbon  atoms 
are  joined  by  two  or  more  bonds.  The  compounds  in  such 
a  series  are  said  to  be  unsaturated.  Ethylene,  C2H4,  is  the 
simplest  unsaturated  carbon  compound.  In  such  unsatu- 
rated compounds,  it  is  believed  that  two  adjacent  carbon 
atoms  are  connected  by  a  double  bond,  because  an  atom  of 
a  halogen  element,  like  bromine,  can  be  added  to  each, 
without  the  replacement  of  hydrogen.  The  graphic  for- 
mulas of  ethylene  and  ethylene  dibromide  represent  this: 

H    H  H     H 

II 
Br—  C—  C—  Br 


I 
C= 

i  A 


ethylene  ethylene  dibromide 

188.   Ethylene  Series.  —  This  series  of  unsaturated  hydro 
carbons  is  represented  by  the  general  formula  CnH2w. 


NAME 

FORMULA 

BOILING  POINT 

Ethylene    
Propylene  -.-  ••• 

C2H4 

-  103°  C. 

-  48.5° 

Butylene     '  . 

C4Hfi 

-  5.0° 

Amylene    

^48 

+  35° 

210  CARBON   COMPOUNDS 

Chemists  have  been  unable  to  prepare  the  theoretical 
methylene,  CH2,  which  would  be  the  first  member  of  the 
series. 

Ethylene,  the  most  important  member  of  the  series,  is 
formed  by  the  destructive  distillation  of  non-volatile 
organic  compounds.  It  is  found  in  natural  gas,  coal  gas, 
and  enriched  water  gas.  The  luminosity  of  illuminating 
gas  is  largely  due  to  the  3  %  or  4  cr/0  of  ethylene  they  con- 
tain. Ethylene  is  more  reactive  than  ethane,  the  corre- 
sponding member  of  the  paraffin  series,  and  has  a  lower 
kindling  temperature.  It  was  formerly  called  olefiant  gas, 
which  means  "oil-forming."  This  was  because  of  the  fact 
that  ethylene  gives  an  oily  liquid  when  it  reacts  with 
chlorine. 

189,  Acetylene  Series.  —  In  this  series  of  hydrocarbons, 
two  of  the  adjacent  carbon  atoms  are  joined  by  a  triple 
bond,  and  the  general  formula  is  CnH2n_2.     The  first  and 
only  important  member  of  the  series  is  acetylene,  C2H2, 
and  its  graphic  formula  is  H  —  C= C  —  H.     The  preparation 
and  uses  of  this  compound  have  already  been  discussed  in 
§§  99  and  119.     Acetylene  is  also  formed  in  small  quanti- 
ties in  the  incomplete  combustion  which  takes  place  when 
a  bunsen  burner  strikes  back.     The  odor  noticed  at  such 
times,  however,  is  due  to  other  gaseous  products. 

SUBSTITUTION  PRODUCTS 

190.  Formation.  —  Chlorine,  bromine,  and  iodine  (halo- 
gen elements)  react  with  methane  to  form  compounds  by 
the  element  replacing  one  or  more  hydrogen  atoms  in  the 
hydrocarbon.     The  reaction  between  methane  and  chlorine 
is  so  violent  that  it  is  necessary  to  regulate  it  by  having 
the  reaction  take  place  in  diffused  sunlight,  or  by  diluting 
the  mixture  of  the  two  combining  gases  with  some  inert 


CHLOROFORM  OR    TRICHLORMETHANE         211 

gas  such  as  carbon  dioxide.  The  substitution  products 
are  named  according  to  the  number  of  halogen  atoms  re- 
placing the  hydrogen.  Thus  from  chlorine  and  methane, 
CH4,  are  formed  : 

CHgCl,    monochlormethane 
CH2C12,  dich  lor  methane 
CHClg,   trichlormethane 
CC14,       tetrachlormethane 

Similarly,  bromine  forms  the  brom -methanes,  CH3Br, 
CH2Br2,  CHBr3,  and  CBr4. 

Although  many  of  the  chlorine  and  bromine  compounds 
may  be  formed  by  direct  substitution,  indirect  methods 
are  often  more  practical.  The  iodine  substitution  prod- 
ucts of  methane,  CH3I,  CH2I2,  CHI3,  and  CI4,  are  always 
made  by  indirect  methods. 

From  the  large  number  of  hydrocarbons  known,  it  is 
possible  to  obtain  numerous  halogen  substitution  products; 
few  of  them,  however,  are  of  practical  importance.  The 
more  useful  of  these  are  described  in  the  sections  that 
follow. 

191.  Monochlormethane  or  Methyl  Chloride. — This   com- 
pound, CH3C1,  is  a  colorless  gas  with  an  ethereal  odor. 
It  is  easily  liquefied  under  atmospheric  pressure  at  —  24°  C. 
The  liquid  is  sometimes  used  in  minor  surgical  operations, 
as  its  rapid  evaporation  deadens  sensibility  by  chilling  the 
affected  part. 

192.  Chloroform  or  Trichlormethane,  CHC13,  was  first  made 
on  a  large  scale  by  distilling  a  water  solution  of  alcohol 
with  bleaching   powder.       Now  it  is  generally  obtained 
commercially  by  distilling  acetone  with  bleaching  powder. 

Chloroform  is  a  heavy,  volatile  liquid,  boiling  at  61°  C., 


212  CARBON  COMPOUNDS 

but  it  is  not  inflammable.  It  has  a  sweet  taste  and  a  char- 
acteristic ethereal  odor.  While  it  is  only  slightly  soluble 
in  water,  it  is  miscible  with  most  of  the  organic  solvents. 
Chloroform  decomposes  slowly  when  exposed  to  light  and 
air,  giving  products  that  are  more  poisonous  than  the 
chloroform.  To  prevent  this  decomposition,  commercial 
chloroform  usually  contains  1  %  of  ethyl  alcohol. 

The  use  of  chloroform  as  an  anaesthetic  has  diminished, 
as  ether  is  safer  in  many  cases.  Chloroform  is  an  excel- 
lent cleansing  agent,  but  its  principal  use  is  as  a  solvent 
for  organic  compounds.  Rubber  is  dissolved  by  it. 

193.  lodoform,  CHI3,  is  a  light  yellow  powder  with  a 
distinctive  odor.     It  is  made  by  adding  iodine  to  a  warm 
aqueous   solution   of   ethyl   alcohol,   made   alkaline  with 
sodium  hydroxide  or  sodium  carbonate.     The   iodoform 
separates  out  as  a  yellow  precipitate.      This  reaction  is 
often  used  as  a  test  for  ethyl  alcohol,  but  is  not  reliable 
when  certain    other  organic  compounds,  as   acetone,  are 
present,  since  these  compounds  give  the  same  result. 

The  antiseptic  properties  of  iodoform  led  to  its  use  in 
surgical  dressings.  To  hide  the  disagreeable  and  per- 
vasive odor,  iodoform  is  generally  put  up  in  some  mixture. 
"Eka-iodoform"  contains  iodoform  and  paraformaldehyde; 
"amozel,"  iodoform  and  thymol.  "Di-iodoform  "  is  tetra- 
iodo-ethylene,  C2I4. 

194.  Carbon  Tetrachloride,  CC14,  is  the  final  result  of  the 
chlorination  of  methane  (§  190).     It  is  made  commercially 
by  the  action  of   chlorine  on  carbon   disulphide,  in   the 
presence  of  antimony  pentasulphide,  Sb2S5,  which  is  not 
permanently  changed  in  the  reaction  : 

CS2  +  3C12   —>-   CC14     +     S2C12 

carbon        chlorine  carbon  sulphur 

disulphide  tetrachloride          chloride 


CHARACTERISTICS   OF  ALCOHOLS  213 

Carbon  tetrachloride  is  a  heavy  liquid,  boiling  at  77°  C., 
and  has  an  odor  not  unlike  that  of  chloroform.  It  readily 
dissolves  greases,  gums,  and  resins.  As  a  non-combustible 
solvent,  the  tetrachloride  finds  wide  use  in  technical  and 
manufacturing  operations.  Mixed  with  gasoline  or  ben- 
zine, it  is  sold  as  a  cleaning  fluid  under  various  trade 
names,  such  as  "  Carbona."  Such  mixtures  are*  non-inflam- 
mable. Tetrachloride  is  the  important  constituent  of  the 
fluid  in  some  small  portable  fire  extinguishers,  for  example 
"Pyrene." 

ALCOHOLS 

195.  General  Characteristics.  —  The  alcohols  are  hydroxyl 
derivatives  from  the  hydrocarbons.  They  may  be  made 
by  the  substitution  of  one  or  more  hydroxyl  groups  for  a 
corresponding  number  of  hydrogen  atoms  in  a  hydro- 
carbon. As  a  rule,  two  hydroxyl  groups  do  not  become 
attached  to  one  carbon  atom.  The  substitution  is  not  a 
direct  one,  however,  as  it  requires  two  steps.  The  com- 
mon alcohols  are  not  obtained  commercially  in*  this  way. 

H  H  H    H  H    H 

H— C— H     H— C— OH     H— C— C— H    H— C— C— OH 

i        i         U       H 

methane  methyl  alcohol  ethane  ethyl  alcohol 

The  group  CH3~  (methyl)  occurs  in  many  carbon  com- 
pounds, as  does  ethyl,  C2H5~.  In  other  words,  these 
groups  are  organic  radicals  and  the  recognition  of  these 
radicals  aids  greatly  in  naming  many  carbon  compounds. 
Among  other  radicals  of  this  class  of  frequent  occurrence 
are  :  propyl,  C3H7~  ;  butyl,  C4H9"~  ;  and  pentyl  or  amyl, 
C5Hn". 

The  alcohols  show  many  resemblances  to  the  metallic 


214  CARBON   COMPOUNDS 

hydroxides  or  bases,  but  the  basic  properties  of  the 
alcohols  are  not  so  well  marked.  Although  they  combine 
with  acids  to  form  salts,  the  combination  takes  place 
slowly,  and  often  special  means,  such  as  increase  in  tem- 
perature, have  to  be  employed  to  effect  the  union.  More- 
over, in  water  solution  the  alcohols  are  not  ionized 
sufficiently  to  affect  litmus  paper. 

In  the  inorganic  bases,  the  metal  is  combined  with  one  or 
more  hydroxyl  groups,  as  NaOH,  Ca(OH)2,  and  Fe(OH)3. 
In  the  case  of  organic  bases,  the  organic  radical  is  combined 
with  hydroxyl/ as  CH3OH,  C2H6OH,  and  C3H5(OH)3. 
Such  organic  radicals  as  methyl,  CH3~,  ethyl,  C2H5~  and 
glyceryl,  C3H5",  because  of  their  positive  (basic)  nature, 
are  termed  alkyl  radicals  or  groups.  R  is  a  general  symbol 
used  for  an  alkyl  radical.  The  general  formula  for  an 
alcohol  is  R-OH. 

196.  Methyl  or  Wood  Alcohol,  CH3OH,  is  obtained  com- 
mercially by  the  destructive  distillation  of  wood  (§  867). 
It  is  a  colorless  liquid  with  a  distinctive  odor  and  boils  at 
66°.  Not  only  does  it  mix  readily  with  water  in  all  pro- 
portions, but  it  dissolves  many  other  substances. 

The  solvent  action  of  wood  alcohol  is  used  in  the  prep- 
aration of  many  shellacs  and  varnishes.  It  burns  with  a 
clean  flame  of  high  heat  value,  and  is  suitable  for  use 
in  the  spirit  lamps  of  curling  irons  and  chafing  dishes. 
Crude  wood  spirit  is  used  for  denaturing  grain  alcohol. 
Methyl  alcohol  is  useful  in  the  preparation  of  formalde- 
hyde, aniline  dyes,  and  many  other  organic  compounds. 

Wood  alcohol  is  a  deadly  poison.  In  confined  and 
poorly  ventilated  places,  even  the  fumes  of  it  have  caused 
fatal  prostration^among  men  using  varnishes  containing  it. 
Paralysis  of  the  optic  nerve  is  one  effect  of  wood  alcohol 
poisoning.  Many  cases  of  total  blindness  have  been  caused 


ETHYL    OR   GRAIN  ALCOHOL  215 

by  the  drinking  of  cheap  whiskies  adulterated  with  wood 
alcohol.     Even  its  use  in  bathing  is  dangerous. 

197.  Ethyl  or  Grain  Alcohol,  C2H5OH,  is  a  product  ob- 
tained from  the  fermentation  of  sugars.  Among  the 
fermentable  sugars  are  sucrose  or  cane  sugar,  found  in 
the  sugar  cane  and  in  the  sugar  beet;  dextrose  and  levulose 
(fructose)  which  occur  in  fruits  and  vegetables.  Dextrose 
is  commonly  known  as  grape  sugar,  on  account  of  its  occur- 
rence in  grapes.  Although  dextrose  and  levulose  have 
the  same  formula,  C6H12O6,  they  are  different  compounds, 
as  the  atoms  are  arranged  differently  in  their  molecules. 
A  very  important  sugar  for  making  alcohol  is  maltose, 
C12H22On  •  H2O.  This  sugar  is  obtained  from  starch  by 
the  action  of  diastase,  a  substance  produced  in  fermenta- 
tion, which  acts  as  a  catalytic  agent.  In  this  country, 
alcohol  is  made  largely  from  the  starch  contained  in  corn, 
rye,  or  barley.  Abroad,  potatoes  and  molasses  are  more 
widely  used.  Diastase  is  contained  in  malt,  which  is  pre- 
pared by  allowing  barley  to  sprout  in  a  warm,  moist  at- 
mosphere, and  then  heating  the  sprouted  grain  to  stop  its 
growth. 

The  technical  preparation  of  alcohol  takes  place  in  the 
following  steps: 

(1)  The  grain  is  ground,  after  it  has  been  heated  in 
order  to  burst  the  covering  of  the  starch  granules.     Then 
it  is  mixed  with  a  small  amount  of  malted  grain. 

(2)  The  diastase  in  the  malt  converts  the  starch  into 
maltose : 

2  C6H1006  +  2  H20  — >-  C13H220U  -  H2O 

starch  water  maltose 

The  malted  mixture  is  agitated  meanwhile  with  water  at 
63°  C.,  as  this  is  the  best  temperature  for  the  conversion. 


216 


CARBON   COMPOUNDS 


(3)  The  liquid  is  then  cooled,  diluted  with  water,  and 
yeast  added.  Yeast  is  a  microscopic  vegetable  organism 
growing  in  chains  of  oval-shaped  cells  (Fig.  77).  Dur- 


a  b 

FIG.  77. — YEAST  CELLS,  HIGHLY  MAGNIFIED:    a,  living;  b,  dead. 

ing  the  process  of  its  growth,  the  yeast  forms  a  ferment 
known  as  zymase.  This,  acting  as  a  catalytic  agent, 
brings  about  the  following  reaction : 


CUH 


M0U  • 

maltose 


H20 


4  C2H5OH 

alcohol 


+  4  C02 

carbon  dioxide 


This  fermentation  takes  from  three  to  nine  days  and 
occurs  best  in  a  solution  containing  about  10  %  sugar. 

(4)  The  fermented  liquid,  containing  from  10%  to 
13%  of  alcohol,  is  distilled  or  rectified  in  an  apparatus  so 
efficient  that  two  distillations  yield  an  alcohol  containing 
but  5  %  of  water. 

When  molasses  (cane  sugar)  is  used,  the  process  is 
similar,  except  that  no  malt  is  necessary.  The  cane  sugar 
is  first  converted  into  dextrose  and  levulose  by  a  ferment 
also  produced  by  the  yeast  plant,  known  as  invertase : 

C12H22°11  +  H2°  — *•  C6H12°6  +  C6H12°6 
cane  sugar          water  dextrose  levulose 

Then  the  zymase  from  the  yeast  brings  about  the  alcoholic 
fermentation  of  the  two  simple  sugars: 


C6H12O6 

dextrose  or 
levulose 


2C2H5OH 

alcohol 


+   2C02 

carbon  dioxide 


DENATURED  ALCOHOL  217 

198.  Properties  of  Ethyl  Alcohol.  —  This  alcohol  is  a  col- 
orless liquid  of  characteristic  odor,  with  a  specific  gravity 
four  fifths  that  of  water.     It  is  miscible  with  water  in  all 
proportions,  the  mixing  being  attended  with  contraction 
of  volume  and  the  evolution  of  some  heat. 

Ordinary  alcohol  contains  5  %  by  volume  of  water. 
This  is  because  the  process  of  fractional  distillation  of 
dilute  alcohol  does  not  yield  an  alcohol  more  concentrated 
than  95%,  since  this  is  a  constant  boiling  mixture. 

Alcohol  is  a  poison,  although  small  quantities  can  be 
taken  into  the  body,  where  it  is  oxidized  and  produces 
heat. 

199.  Uses  of  Ethyl  Alcohol.  —  Alcohol  has  many  minor 
uses  in  the  household.     On  account  of  its  rapid  evapora- 
tion, it  is  used  extensively  to  reduce  the  temperature  of 
feverish  patients.     Its  solvent  power  leads  to  a  wide  range 
of  uses.     Pharmacists  find  it  invaluable  in  the  preparation 
of  tinctures,  essences,  extracts,  and  many  medicinal  prep- 
arations.    Many  of  the  better  grades  of  shellacs  and  var- 
nishes  contain   ethyl   alcohol.     The    use    of    alcohol    in 
beverages  consumes  large  quantities. 

Among  the  chief  industrial  uses  are  the  manufacture  of 
vinegar,  iodoform,  chloroform,  and  many  other  organic 
compounds.  A  coming  use  is  for  internal  combustion  en- 
gines, as  present  indications  are  that  there  will  not  be 
enough  gasoline  to  meet  all  demands. 

200.  Denatured  Alcohol  is  ethyl  alcohol  to  which  wood 
alcohol  or  other  poisonous  substances  have  been  added,  in 
order  to  make  its  use  for  beverages  or  medicines  impossi- 
ble.    The  internal  revenue  tax  is  11.10  per  gallon  of  proof 
spirit,  which  is  50  %  alcohol.     This  makes  a  tax  of  about 
12.00   for   the    95%  alcohol.     Denatured  alcohol  is   tax 
free,  so  as  to  encourage  its  industrial  use. 


218  CARBON  COMPOUNDS 

Completely  denatured  alcohol,  as  authorized  by  the 
government,  contains : 

100  parts  ethyl  alcohol  (not  less  than  90  %  strength), 

10  parts  methyl  (wood)  alcohol, 

^  part  benzine. 

There  are  also  other  formulas  for  special  purposes  which 
may  be  made  under  government  license. 

201.  Alcoholic  Beverages.  —  These  may  be  classed  as 
(1)  the  direct  products  of  fermentation,  as  beer,  wines, 
and  champagnes,  and  (2)  distilled  liquors,  in  which  the 
fermented  products  are  distilled  to  increase  the  percentage 
of  alcohol. 

Beer  is  made  by  the  fermentation  of  malt,  prepared  as 
described  in  §  197.  The  temperature  is  kept  down  to  5°  C. 
by  refrigeration.  The  yeast  grows  at  the  bottom  of  the 
vat.  The  fermented  liquor  is  filtered,  hops  added  to  give 
a  bitter  taste  and  keeping  qualities,  and  then  water  added 
to  the  desired  concentration.  Beer  contains  from  3  %  to 
5%  of  alcohol.  Rice  and  glucose  are  often  used  to 
replace  the  barley.  In  making  ale,  the  yeast  grows  at  the 
top  of  the  fermenting  liquid,  which  is  kept  at  about  the 
ordinary  temperature.  Ale  contains  from  3%  to  8%  of 
alcohol. 

Wines  are  made  by  the  fermentation  of  sugars  in  fruit 
juices,  particularly  those  of  the  grape.  Various  ferments 
are  peculiar  to  different  wine-producing  regions.  The 
wine  is  kept  for  some  time  to  allow  the  tannin  and  other 
substances  to  precipitate,  as  well  as  to  allow  certain  other 
compounds  to  react  and  produce  substances  which  give  an 
agreeable  flavor.  Claret,  Rhine  wines,  and  sauternes  con- 
tain from  7%  to  12%  of  alcohol.  Port,  sherry,  and 
Madeira  contain  from  15%  to  20%.  These  last  three 
wines  are  generally  fortified,  that  is,  alcohol  is  added  to 


ALCOHOLIC  BEVERAGES  219 

the  fermented  liquid  to  obtain  the  desired  percentage. 
Fermentation  does  not  give  more  than  17  %  alcohol,  as  at 
that  concentration  the  yeast  cells  are  killed. 

Champagne  is  made  by  conducting  the  fermentation  in 
corked  bottles,  the  process  taking  from  6  months  to  2 
years.  The  bottles  are  tilted  mouth  downwards,  so  that 
the'  sediment  will  collect  in  the  neck.  Finally  the  bottle 
is  opened  for  a  moment,  in  order  to  blow  out  the  sediment. 
Next  a  little  sugar  solution  is  added  to  fill  the  bottle, 
which  is  then  corked  and  stored  until  the  champagne  is 
deemed  to  have  a  uniform  composition.  The  alcohol  con- 
tent is  from  8%  to  11%.  Imitation  champagnes  are  made 
by  saturating  white  wines  with  carbon  dioxide  under 
pressure. 

Whisky  is  made  by  distilling  a  beer  made  from  rye, 
corn,  or  barley.  It  is  stored  in  wooden  barrels  until' the 
desired  flavor  is  obtained  and  the  fusel  oil  disappears. 
Fusel  oil  is  chiefly  a  mixture  of  the  two  amyl  alcohols 
C6HUOH.  Whisky  contains  from  25  %  to  45  %  of  alcohol, 
and  gets  its  flavor  from  materials  in  the  malted  grain  and 
from  the  wooden  kegs  in  which  it  is  stored. 

Brandy  is  made  by  distilling  wine,  or  the  fermented 
juices  of  apples,  peaches,  cherries,  or  other  fruits.  It  con- 
tains from  40  %  to  50  %  of  alcohol.  Grin  is  prepared  by 
the  distillation  of  an  alcoholic  liquor  made  from  grain. 
The  final  distillation  takes  place  with  juniper  berries  or 
anise  seed,  so  as  to  get  the  characteristic  flavor.  Gin 
usually  contains  about  30  %  of  alcohol.  Rum  is  made  by 
distilling  the  liquid  obtained  by  ferrnenting  molasses. 
The  percentage  of  alcohol  contained  varies  from  40  %  to 
80  %.  Liqueurs  or  cordials  are  made  by  steeping  fruits  or 
aromatic  herbs  in  alcoholic  liquors  and  then  distilling. 
Sirup  is  then  added  to  the  product,  and  often  coloring 
matter  as  well. 


220  CARBON  COMPOUNDS 


SUMMARY 

Hydrocarbons  are  compounds  containing  only  hydrogen  and 
carbon. 

Paraffin  Series  of  Hydrocarbons  have  the  general  formula 
CnH2n+2.  Methane,  CH4,  is  the  simplest  member  of  this  series. 

Unsaturated  Series  of  Hydrocarbons  are  typified  by  the  ethylene 
series,  CnH2n,  and  the  acetylene  series,  Cn\i.2n_2.  Acetylene,  C2H4, 
is  the  first  member  of  the  latter  series. 

Substitution  Products  of  hydrocarbons  are  formed  by  the 
replacement  of  one  or  more  hydrogen  atoms  by  a  corresponding 
number  of  .atoms  of  such  elements  as  chlorine,  bromine,  and 
iodine.  Chloroform,  CHC13,  and  iodoform,  CHI3,  are  important 
substitution  products. 

Alcohols  are  hydroxyl  derivatives  of  the  hydrocarbons.  They 
consist  of  some  such  alkyl  radical  as  methyl,  CH3~,  or  ethyl, 
C2H5~,  in  union  with  one  or  more  hydroxyl  groups.  Important 
alcohols  are  methyl  or  wood  alcohol,  CH3OH,  ethyl  or  grain 
alcohol,  C2H5OH,  and  glycerin,  C3H5(OH)3.  Alcohol  results  from 
the  conversion  by  fermentation  of  a  sugar  into  an  alcohol  and 
carbon  dioxide. 

Denatured  Alcohol  is  grain  alcohol  rendered  unfit  for  beverages 
and  medicines  by  the  addition  of  some  poisonous  substance,  as 
wood  alcohol  or  benzine. 

EXERCISES 

1.  Give  two  reasons  for  the  number  and  complexity  of  car- 
bon compounds. 

2.  Write  the   graphic  formulas  for  the  three  possible  pen- 
tanes,  C5H12. 

3.  What  is  marsh  gas?     Fire  damp? 

4.  What  is  an  unsaturated  hydrocarbon?     Give  the  name 
and  graphic  formula  for  one. 


EXERCISES  221 

5.  Write  an  equation  for  the  preparation  of  acetylene. 

6.  Give  the  name,  formula,  and  an  important  use  of  each 
of  three  halogen  substitution  products. 

7.  What  are  the  advantages  of  carbon  tetrachloride  as  a 
cleaning  fluid  ? 

8.  What  is  an  alkyl  radical?     Give  names  and  formulas 
for  two  common  ones. 

9.  What  are  alcohols  ?    How  do  they  differ  from  inorganic 
bases  ? 

10.  Why  should  varnishes  made  with  wood  alcohol   have 
this  fact  printed  on  the  container  ? 

11.  State  the  catalytic  action  brought  about  by  each  of  the 
following :  diastase,  invertase,  and  zymase. 

12.  Write  two  equations   showing  the  formation  of  ethyl 
alcohol  from  (a)  starch,  (6)  cane  sugar. 

13.  How  is  alcohol  obtained  from  fermented  liquids? 

14.  Show  how  the  properties  of  ethyl  alcohol  lead  to  its  im- 
portant uses. 

15.  What  is  denatured  alcohol?     Why  is  it  made? 


CHAPTER    XX 
CARBON  COMPOUNDS 

Aldehydes,  Acids,  Esters,  and  Carbohydrates 

ALDEHYDES 

202.  Characteristics.  —  Aldehydes  are  made  by  removing 
two  hydrogen  atoms  from  an  alcohol.  The  name  aldehyde 
is  derived  from  this  process  (alcohol  c?e%<#rogenatus). 

The  removal  of  the  hydrogen  is  accomplished  by 
oxygen,  hence  aldehydes  are  oxidation  products  of  alcohols. 
Thus,  methyl  alcohol  is  oxidized  to  formaldehyde : 

CH3OH    +    O    — »-   HCHO    +  H20 

methyl  alcohol      oxygen  formaldehyde       water 

Further  oxidation  changes  an  aldehyde  to  an  acid,  the 
aldehyde  taking  its  name  from  the  acid  into  which  it  oxi- 
dizes. The  following  shows  the  relations  of  the  two 
simplest  aldehydes: 

CH3OH     methyl  alcohol         C2H5OH  ethyl  alcohol 

oxidizes  to    L  oxidizes  to       J, 

HGHO      formaldehyde       C2H5CHO  acetic  aldehyde 

oxidizes  to    1,  oxidizes  to        \. 

HCOOH     formic  acid         C2H5COOH  acetic  acid 

An  aldehyde  does  not  contain  a  hydroxyl  group.  The 
general  formula  for  aldehydes  shows  this: 

H 

I 

R-C  =  0 

R  stands  for  an  alkyl  radical,  as  methyl,  CH3~,  ethyl, 
C2H5-  etc. 


FORMA  LDEH  YDE 


223 


203.  Formaldehyde.  —  This  simplest  aldehyde  is  made 
practically  by  burning  methyl  alcohol  in  a  limited  supply 
of  air.  The  air  is  drawn  through  methyl  alcohol  warmed 
to  about  45°.  The  mixture  of  air  and  alcohol  vapor  then 
passes  over  a  heated  copper  spiral.  Soon  the  heat  of  the 
reaction  producing  the  formaldehyde  keeps  the  copper  hot 
enough  to  bring  about  the  oxidation  of  the  alcohol  vapors. 
The  gases  are  condensed  to  a  liquid  containing  formal- 
dehyde, water,  and  some  methyl  alcohol.  By  proper  reg- 
ulation, a  solution  containing  40%  formaldehyde  can  be 
made  by  this  process.  The  product  is  known  as  formalin. 


FIG.  78. 
Formaldehyde  candle  for  fumigation.      Box  removed  to  show  candle. 

Formaldehyde  is  a  gas  with  a  stinging,  stifling  odor, 
and  causes  the  eyes  to  smart.  It  liquefies  at  —  21°  C. 
Both  the  moist  gas  and  its  water  solution  are  powerful 
germicides.  Specially  constructed  lamps  for  burning 
methyl  alcohol  in  an  insufficient  supply  of  air  were  used 
for  producing  formaldehyde  for  disinfection.  Tablets,  or 
candles,  of  formacone  (Fig.  78)  are  now  generally  used. 
Formacone  is  a  white,  crystalline  solid,  made  by  heating 
the  water  solution  of  formaldehyde,  or  by  evaporating  the 
solution  with  sulphuric  acid.  A  number  of  formaldehyde 
molecules  unite  to  form  the  complex  molecule  (HCHO),,. 


224  CARBON  COMPOUNDS 

of  formacone,  whose  structure  is  not  known.  When 
formacone  is  heated,  or  boiled  with  water,  formaldehyde 
is  evolved. 

Sometimes  in  public  places  small  quantities  of  formalin 
are  sprayed  into  the  air.  More  frequently,  specially 
devised  machines  continually  furnish  small  amounts  of 
formaldehyde  gas  to  the  air,  as  a  deodorizer  and  disin- 
fectant. Formaldehyde  does  not  produce  the  undesirable 
bleaching  effect  of  sulphur  dioxide,  when  used  for 
fumigation. 

Among  other  uses  of  formaldehyde  are  the  preservation 
of  anatomical  specimens,  the  hardening  of  gelatin  films 
for  photographic  plates,  and  the  objectionable  employment 
as  a  food  preservative. 

ORGANIC  ACIDS 

204.  Characteristics.  —  As  shown  in  §  202,  the  oxida- 
tion of  an  alcohol  gives  an  aldehyde.  Further  oxidation 
changes  the  aldehyde  to  an  acid.  The  organic  acids, 
then,  are  oxidation  products  of  the  alcohols.  Thus,  acetic 
acid  is  made  from  ethyl  alcohol.  A  comparison  of  the 
formulas  shows  that  one  oxygen  atom  has  replaced  two 
hydrogen  atoms : 

CH3  .  CH2OH  ethyl  alcohol  (C2H5OH) 
CH3  .  COOH    acetic  acid       (HC2H3O2) 

The  introduction  of  the  oxygen  atom  gives  an  acid  char- 
acter to  the  molecule  formed.  The  group  —COOH  is 
known  as  carboxyl.  The  organic  acids  may  be  regarded 
as  carboxyl  derivatives  of  the  hydrocarbons.  The  union 
of  an  alkyl  radical,  like  methyl  or  ethyl,  with  hydroxyl 
gives  an  alcohol,  a  substance  with  properties  resembling 
a  base.  An  alkyl  radical  with  carboxyl  gives  an  organic 
acid.  The  organic  acids  have  many  properties  in  common 


ACETIC  ACID 


225 


with  the  inorganic  acids,  but  are  much  less  active  as  a 
class.     They  have  the  general  formula  : 

R_C-OH 

II 
O 

205.  Fatty  Acids. — The  acids  containing  but  one  car- 
boxyl  group,  and  derived  from  the  paraffin  series  of 
hydrocarbons,  are  known  as  fatty  acids.  Some  of  those 
first  isolated  were  obtained  by  the  decomposition  of  cer- 
tain fats. 

SOME  FATTY  ACIDS 


NAME 

FORMULA 

MELTING 
POINT 

OCCURRENCE 

Formic  acid    . 

H  .  COOH 

8.3°  C. 

Red  ants 

Acetic  acid 

CH3.COOH 

16.6°  C. 

Sorrel  ;  fruit  juices 

Propionic  acid 

C2H5.COOH 

-36°C. 

Butyric  acid   . 

CgH7-COOH 

-2°C. 

Rancid  butter 

Valeric  acid    . 

C4H9.COOH 

-  58.5°  C. 

Valerian  wood 

Caproic  acid  . 

C5Hn.COOH 

-1.5°C. 

Rancid  cocoanut  oil 

Palmitic  acid  . 

C15H31.COOH 

62.6°  C. 

As  salts  (esters)  in  ani- 

Margaric acid 

C16H33.COOH 

60°  C. 

mal  and  vegetable  oils 

Stearic  acid     . 

C17H35-COOH 

963°  C. 

and  fats 

206.    Acetic  Acid.  — Acetic  acid, 

H(C2H3O2)  or  CH3COOH, 

is  obtained  in  quantity  from  the  destructive  distillation 
of  wood  (§  367).  Commercial  acetic  acid  is  a  liquid 
which  contains  50%  of  H(C2H3O2).  Glacial  acetic  acid 
contains  less  than  1  %  of  water.  When  it  is  pure,  it  boils 
at  119°  C.,  and  solidifies  at  16.6°  to  an  icelike  solid,  to 
which  fact  it  owes  its  name.  The  glacial  acid  has  a  very 
penetrating  odor  and  is  an  excellent  solvent  for  many 
organic  salts. 


226  CARBON   COMPOUNDS 

Acetic  acid  can  also  be  obtained  by  the  oxidation  of 
grain  alcohol : 

C2H6OH  +    02  -+  HC.H.O,  +  H20 

ethyl  alcohol       oxygen  acetic  acid  water 

The  reaction  is  brought  about  in  dilute  alcohol  solutions 
by  acetic  acid  bacteria  (Fig.  79)  (mother  of  vinegar)  in 
the  presence  of  oxygen  from  the  air.  By  this  acetic  acid 
fermentation,  vinegar  is  made  from  dilute  solutions  of 
alcohol,  as  wine,  cider,  or  the  liquid  from  fermented  malt. 
The  process  takes  several  weeks,  as  the  absorption  of 

oxygen  takes  place  at  the  surface 

**^  of  the  liquid  only.     The  vinegar 

f £  obtained   contains  from   6%   to 

W     10%    of  acetic  acid,  as  well  as 

•~^c  "*£       '^f*-'^       certain     natural    coloring    and 

flavoring  materials. 

FIG.  79.  — ACETIC  ACID  BACTERIA.  ° 

(Magnified  4000  diameters.)  In   the  9™*  Vme9ar  Process'  a 

solution  containing  about  10% 

alcohol  is  allowed  to  trickle  over  beech  wood  shavings 
loosely  filling  large  vats,  through  which  air  circulates. 
The  shavings  are  first  drenched  with  old  vinegar,  so  as  to 
insure  the  presence  of  the  fermenting  organism.  The 
process  takes  about  ten  days  and  the  product  contains 
from  4  %  to  6  %  of  acetic  acid.  As  the  vinegar  obtained 
is  often  a  colorless  liquid,  coloring  and  flavoring  materials 
are  added. 

ESTERS   OR  ETHEREAL  SALTS 

207.  Formation.  —  Esters  are  an  important  class  of 
organic  compounds.  They  occur  widely  distributed  in 
nature,  giving  the  characteristic  odors  to  many  flowers 
and  fruits.  Many  of  the  esters  are  readily  volatile  liquids, 
a  fact  which  suggested  the  name  ethereal  salts.  Banana 


ESTERIFICATION  227 

oil,  often  used  in  aluminum  paint,  is  amyl  acetate  ;  oil  of 
wintergreen  is  methyl  salicylate. 

Esters  are  formed  by  a  reaction  corresponding  to  the 
formation  of  an  inorganic  salt  by  neutralization  : 

base  acid  salt  water 

KOH    +  HNO3  —  ^       KNOg    +  HOH 

potassium       nitric  acid  potassium 

hydroxide  nitrate 


alcohol          acid  ester  water 

C2H5OH  +  HNO3  -7-*-  C2H5NO3  +  HOH 

ethyl  alcohol       nitric  acid  ethyl  nitrate 


This  reaction  of  an  alcohol  and  an  acid  to  produce  an  ester 
and  water  is  termed  esterification.  Unlike  a  true  neutrali- 
zation, the  reaction  proceeds  slowly  at  ordinary  tempera- 
tures, but  is  accelerated  by  heating.  As  the  reaction  is 
a  reversible  one,  it  does  not  run  to  completion,  unless 
some  dehydrating  agent,  as  concentrated  sulphuric  acid 
or  hydrogen  chloride,  is  present  to  take  up  the  water 
formed.  Esterification  may  be  described  as  the  reaction 
of  an  alcohol  with  an  acid,  brought  about  by  the  elimina- 
tion of  water. 

208.  Chemical  Properties.  —  Although  the  esters  re- 
semble inorganic  salts  in  the  method  of  their  formation, 
their  chemical  properties  are  quite  unlike.  Most  of  the 
inorganic  salts  are  highly  ionized  (§  406)  and  take  part 
readily  in  reactions  of  double  replacement.  The  esters 
are  not  ionized  and  their  reactions  are  often  different  from 
those  of  double  replacement.  The  esters  resemble  most 
closely  the  inorganic  salts  formed  from  a  weak  acid  or 
a  weak  base.  Like  them,  they  are  easily  decomposed 
(hydrolyzed)  with  water  : 


228  CARBON   COMPOUNDS 

KCN   +   HOH  ^±:    KOH   +   HCN 

potassium  water  potassium      hydrocyanic 

cyanide  hydroxide  acid 

C2H5C2H302  +   HOH  ^±  C2H5OH  +  H(C2H3O2) 

ethyl  acetate  water  ethyl  alcohol  acetic  acid 

In  this  hydrolysis,  water  splits  the  ester  into  the  alcohol 
and  acid  from  which  it  was  formed.  This  process  is 
saponification  and  is  very  important  in  soap  making 
(§  211).  Saponification  takes  place  most  completely 
when  the  water  is  hot,  under  pressure,  or  in  the  presence 
of  alkalies  or  acids. 

209.  Esters  of  Inorganic  Acids.  —  The  esters  of  the  strong 
inorganic  acids  can  be  prepared  by  the  action  of  the  acid 
with  an  alcohol,  although  certain  precautions  are  often 
necessary.     The  esters  of  the,  weak  inorganic  acids    are 
prepared  by  special  methods. 

Among  some  of  the  well-known  esters  of  inorganic  acids 
are  ethyl  nitrite,  C2H5NO2,  whose  alcoholic  solution  is 
the  medicinal  "  sweet  spirits  of  niter " ;  amyl  nitrite, 
C5HnNO2,  also  used  in  medicine  ;  and  glyceryl  nitrate, 
CgH6(NO3)3,  which  is  more  familiarly  known  as  the  ex- 
plosive nitroglycerin.  This  is  made  from  glycerin. 

210.  Hydrogenation  of  Oils.  —  The    supply   of    lard    for 
cooking  purposes   has   not  kept   pace  with   the  demand. 
Olive  oil  is  too  expensive  a  substitute,  and  cottonseed  oil 
has  certain  objectionable  qualities  when  so  used.     Hence 
the  manufacture  of  substitutes  for  lard  has  become  com- 
mon.    In  making  these,  large  quantities  of  the  hard  fat, 
stearin  (§  211),  obtained  as  a  by-product  of  the  oleomar- 
garine factories,  have  been  used.     Recently  a  method  has 
been  discovered  for  the  hydrogenation  of  oils  which  are 
composed  of  unsaturated  acids  and  their  esters.     Thus, 


GLYCERIN  229 

oleic  acid,  in  the  presence  of  a  suitable  catalytic  agent, 
will  combine  with  hydrogen,  forming  a  saturated  com- 
pound : 

C17H83COOH   +   Ha    — >•     C17H35COOH 

oleic  acid  hydrogen  stearic  acid 

By  this  process  an  oil  is  converted  into  a  hard  .fat. 

A  number  of  catalytic  agents  have  been  tried,  but  thus 
far  finely  divided  palladium  and  freshly  reduced  nickel 
have  proved  to  be  the  most  successful.  The  hydrogen  is 
obtained  electrolytically,  or  by  passing  steam  over  re- 
duced, spongy  iron.  One  per  cent  of  hydrogen  by  weight 
converts  cottonseed  oil  into  a  fatty  body  of  the  consist- 
ency of  lard.  The  product  obtained  is  edible. 

Hydrogenation  has  also  proved  of  great  value  to  the 
soap  industries.  Oils  which  formerly  gave  soft  soaps  are 
now  converted  into  compounds  which  yield  the  more  valu- 
able hard  soaps.  Fish  oil  and  whale  pil,  which  have  objec- 
tionable odors,  are  converted  into  deodorized  oils  suitable 
for  soap  making. 

The  hydrogenation  of  oils  is  a  rapidly  developing  in- 
dustry. By  it,  animal  and  vegetable  oils  can  be  converted 
into  fatty  bodies  of  any  desired  consistency,  as  the  process 
admits  of  a  high  degree  of  control.  Its  products  are  not 
only  valuable  to  soap  makers  and  lard  manufacturers,  but 
are  also  useful  in  the  making  of  lubricants  and  other  tech- 
nical products. 

211.  Glycerin,  C3H5(OH)3,  is  an  alcohol  obtained  from 
certain  animal  fats  and  vegetable  oils.  These  are  mixtures 
of  palmatin,  stearin,  and  olein,  which  may  be  considered 
v  as  esters  made  from  the  alcohol,  glycerin,  and  palmitic 
acid  (C15H31 .  COOH),  stearic  acid  (C17H35 .  COOH),  and 
oleic  acid  (C17H33 .  COOH),  respectively.  A  preponder- 
ance of  stearin  gives  the  harder  fats,  as  beef  and  mutton 


230  CARBON  COMPOUNDS 

tallows,  while  a  large  proportion  of  olein  occurs  in  lard, 
olive  oil,  and  cottonseed  oil.  Palm  oil  is  chiefly  palmatin. 
Glycerin  results  from  the  hydrolysis  of  the  glyceryl 
(C3H5)  esters,  the  water  splitting  the  ester  into  an  alcohol 
and  an  acid  (§  208)  : 

(C17H35.  COO)3C3H5  +  3  HOH  ^ 

glyceryl  stearate  water 

03H6(OH)3  +  SCWCOOH 

glycerin  stearic  acid 

This  reaction  is  carried  out  on  a  commercial  scale  by  heat- 
ing the  glyceryl  stearate  and  water  under  pressure  in 
the  presence  of  a  little  lime.  By  this  process  large  quan- 
tities of  glycerin  are  made.  The  other  valuable  product 
of  the  reaction,  stearic  acid,  is  used  for  making  soaps  and 
candles. 

Another  important  source  of  glycerin  is  soap  making,  as 
the  hydrolysis  of  tne  glyceryl  esters  conducted  in  the 
presence  of  an*  alkali,  yields  a  soap  and  glycerin.  The 
process  is  termed  saponiftcation.  Common  soap  is  a  mix- 
ture of  the  sodium  salts  of  the  organic  acids  mentioned 
above.  The  reaction  for  the  saponification  of  stearin  is : 

(C1TH35.COO)3C,H6+     3NaOH    ^± 

glyceryl  stearate  sodium  hydroxide 

3  C1THB  .  COONa  +  0,H6(OH)3 

sodium  stearate  glycerin 

The  glycerin  is  separated  from  the  spent  lye  of  the 
soap  works.  This  liquid  is  run  off,  any  excess  of  soap 
removed,  certain  impurities  precipitated  with  iron  salts, 
and  the  liquid  evaporated,  so  as  to  cause  the  sodium 
chloride  to  crystallize  out.  Superheated  steam  is  passed 
through  the  liquid  residue,  and  carries  the  glycerin  off  with 
it.  The  distillate  is  evaporated  in  vacuum  pans,  to  dis- 


NITROGLYCERIN  231 

pose  of  the  excess  of  water.  This  last  evaporation  is  con- 
tinued until  the  liquid  has  a  specific  gravity  of  1.26. 

Glycerin  is  a  sirupy  liquid  with  a  sweet  taste.  It  is 
miscible  with  water  and  alcohol.  Its  solvent  action 
approaches  that  of  water,  as  it  dissolves  a  great  variety 
of  substances.  Glycerin  is  so  hygroscopic  that  it  will 
absorb  half  its  weight  of  water  from  the  moisture  of  the 
air. 

Glycerin  is  widely  and  extensively  used.  Large  quan- 
tities are  converted  into  nitroglycerin.  Glycerin  is 
used  in  cosmetic  and  medicinal  preparations,  in  the  ink 
rolls  of  printers,  and  in  the  ink  for  rubber  stamps.  It 
is  also  used  to  keep  tobacco  moist  and  to  soften  leather. 
These  uses  are  largely  due  to  its  hygroscopic  properties. 

212.  Nitroglycerin,  C3H6(NO3)3,  is  the  trinitrate  of 
glycerin,  made  by  slowly  adding  glycerin  to  a  mixture 
of  fuming  nitric  and  concentrated  sulphuric  acids,  with 
the  temperature  kept  below  20°  C.  :  . 

C,H.(OH),  +  3  HN08  5±  C3H6(NOS)3  +  3  HOH 

glycerin  nitric  acid  nitroglyceriu  water 

The  sulphuric  acid  does  not  appear  in  the  equation.  Its 
dehydrating  action  causes  the  reaction  to  continue  by 
absorbing  the  water  formed.  The  nitroglycerin  is  drawn 
off  from  the  nitrating  mixture  and  is  washed  with  water 
and  then  with  a  very  dilute  solution  of  sodium  carbonate. 
Nitroglycerin  is  a  heavy,  colorless,  oily  liquid,  and 
freezes  at  about  8°  C.  It  explodes  when  heated  to  180° 
or  when  subjected  to  shock.  For  convenience  in  han- 
dling, it  is  absorbed  by  some  inert,  porous  substance,  such 
as  infusorial  earth,  producing  an  earthy,  powdery  mass. 
The  original  dynamite  of  Nobel  was  made  in  this  way. 
It  is  now  sold  under  the  name  of  75  %  dynamite  or  No.  1 


232  CARBON  COMPOUNDS 

giant  powder.  The  modern  dynamites  are  more  explosive. 
They  contain  about  13  %  wood  pulp,  33  %  nitroglycerin, 
and  54  %  of  some  oxidizing  agent,  such  as  sodium  nitrate. 
Sometimes  the  wood  pulp  itself  is  partly  nitrated.  Dy- 
namites are  classified  and  named  according  to  the  percent- 
age of  nitroglycerin  they  contain. 

G-elatin  dynamite,  or  blasting  gelatin,  is  made  by  dissolv- 
ing 1  part  nitrocellulose  (§  214)  in  9  parts  nitroglycerin. 
This  forms  a  clear  jellylike  mass  resembling  gelatin.  As 
there  is  no  inert  matter,  gelatin  dynamite  is  a  very  power- 
ful explosive.  It  is  particularly  useful  for  heavy  blasting. 

CARBOHYDRATES 

The  carbohydrates  are  an  important  class  of  compounds, 
composed  of  carbon,  hydrogen,  and  oxygen.  The  hydro- 
gen and  oxygen  in  the  molecule  are  in  the  same  proportion 
by  weight  as  they  are  in  water. 

213.  Cellulose  composes  the  cell  walls  of  plants  and  is 
represented  by  the  formula  (CgH^Og)^.  Absorbent 
cotton  and  washed  filter  paper  are  nearly  pure  cellulose. 
It  is  the  main  constituent  of  straw  and  wood.  Cellulose 
may  be  obtained  from  vegetable  fibers  by  several  succes- 
sive treatments  with  chlorine  and  sodium  hydroxide,  in 
order  to  convert  the  compounds  associated  with  it  into 
soluble  ones  that  can  be  removed  by  washing. 

Cellulose  is  soluble  in  Schweitzer's  reagent,  an  am- 
moniacal  solution  of  cupric  hydroxide.  The  addition  of 
hydrochloric  acid  precipitates  the  cellulose.  Waterproof 
paper  is  prepared  by  leaving  paper  a  short  time  in  contact 
with  Schweitzer's  reagent,  which  acts  upon  the  surface. 
Then  the  paper  is  passed  through  heated  rolls  and  dried. 

When  unsized  paper  is  left  for  a  moment  in  contact 


NITROCELLULOSE  233 

with  dilute  sulphuric  acid  (1 : 4),  it  is  converted  into  a 
colloidal  cellulose  known  as  amyloid.  After  washing  with 
water  and  dilute  ammonia,  the  paper  becomes  tougher  and 
has  a  smoother  surface.  This  product  is  known  as  parch- 
ment paper. 

Although  dilute  alkalies  hardly  affect  cellulose,  boiling 
with  more  concentrated  solutions  of  alkali  cause  vegetable 
cellulose  fibers  to  become  rounded  and  swollen  and  to 
assume  a  silky  appearance.  This  is  the  process  of  mercer- 
izing described  in  §  306. 

214.  Nitrocellulose  is  the  earlier  name  given  to  a  set  of 
compounds  which  are  now  generally  regarded  as  true 
nitrates  of  cellulose.  They  are  made  by  replacing  in 
cellulose  from  2  to  6  hydroxyl  groups  by  NO3  groups. 
This  is  accomplished  by  a  mixture  of  concentrated  nitric 
and  sulphuric  acids.  The  degree  of  nitration  of  cellu- 
lose depends  upon  the  concentration  of  the  nitric  and 
sulphuric  acids,  the  temperature,  the  time  of  contact,  and 
the  relative  mass  of  materials.  The  lower  nitrates  are 
known  as  pyroxylin  and  their  solubility  in  a  mixture  of 
alcohol  and  ether  decreases  with  the  number  of  NO3 
groups  introduced.  Collodion  is  such  a  solution  of  py- 
roxylin. On  the  evaporation  of  the  alcohol  and  ether,  a 
tough,  transparent  film  remains.  On  this  account,  collo- 
dion is  used  on  photographic  plates,  for  lacquers,  and  as  a 
liquid  court  plaster.  Celluloid  is  made  by  incorporating 
two  parts  of  pyroxylin  with  one  part  of  camphor.  As 
the  nitrocelluloses  are  explosive  when  heated,  celluloid 
articles  should  not  be  thrown  into  the  stove.  Many 
serious  accidents  have  been  caused  by  doing  this. 

The  treatment  of  dry  cotton  with  concentrated  nitric 
and  sulphuric  acids  under  certain  conditions  yields  the 
hexanitrate,  [C12H14O4(N03)6]tr,  commonly  known  as  gun- 


234  CARBON  COMPOUNDS 

cotton.     The  cellulose  hexanitrate  is  the  basis  of  many  high 
explosives.     It  is  insoluble  in  water,  ether,  or  chloroform. 

215.  Smokeless  Powder.  —  While  wood  pulp  and  paper 
may  be  used  for  making  the  cheaper  explosives  and  cheap 
celluloid,  cleaned  and  bleached  cotton  wool  and  the  waste 
from  cotton  mills  are  employed  in  the  making  of  gun- 
cotton  for  smokeless  powders.     After  the  nitrocellulose  is 
prepared  and  washed  free  from  acids,  it  is  made  into  a 
plastic  mass  with  the  aid  of  a  little  ether-alcohol  mixture. 
This  dough  is  then  run  through  a  machine  which  presses 
it  into  perforated  rods.     The  rods  are  cut  into  grains  of  a 
size  suitable  to  the  gun  in  which  they  are  to  be  exploded. 
Finally  the  powder  is  very  carefully  dried,  so  as  to  reduce 
the  amount  of  volatile  matter  (water,  alcohol,  and  ether). 

Acetone  is  sometimes  used  for  working  the  cellulose 
nitrate  into  a  pasty  mass,  and  nitroglycerin  and  other 
nitre-organic  compounds  are  incorporated  during  the 
making  of  the  smokeless  powder.  Nitrocellulose  powders 
with  a  nitroglycerin  base  are  safer  and  more  uniform  in 
action  than  straight  nitrocellulose  powders.  The  latter, 
however,  are  less  corrosive  to  the  gun.  The  wide  use  of 
smokeless  powders  and  the  demand  for  celluloid  and  its 
allied  articles,  have  made  nitrocellulose  manufacture  one 
of  the  most  extensive  chemical  industries. 

216.  Starch,  (C6H10O5)X,  occurs  as  granules  in  the  cells 
of  nearly  all  plants.     Certain  seeds  and  roots  are  partic- 
ularly rich  in  this  substance.     The  starch  in  seeds  serves 
as  nourishment  for  the  young  plant  until  the  leaves  and 
roots  become  developed  sufficiently  to  draw  plant  food 
from  the  air  and  the  soil. 

The  principal  source  of  starch  in  the  United  States  is 
corn,  while  in  other  countries  potatoes  and  rice  are  the 


PROPERTIES   OF  STARCH  235 

chief  sources  of  supply.  The  general  method  of  ex- 
traction from  corn  includes  soaking,  grinding,  and  wash- 
ing the  material  in  water  and  then  filtering.  In  the  last 
process,  the  finely  divided  starch  passes  through  bolting 
cloth  and  is  recovered  from  the  water  in  which  it  is  sus- 
pended. When  dried,  the  starch  contains  about  10%  of 
water. 

Heating  with  water  causes  the  starch  granules  to  swell 
and  burst  their  enveloping  cellulose  membranes,  forming 
a  gelatinous  mass.  Further  heating  makes  some  of  the 
starch  pass  into  solution.  Soluble  starch,  however,  is 
usually  made  by  treating  starch  with  cold  dilute  acid  for 
several  days. 

Heating  with  dilute  acids  changes  starch  into  dextrin, 
maltose,  and  glucose.  The  action  of  diastase  on  starch 
has  already  been  discussed  in  the  production  of  alcohol 
(§  197).  When  dry  starch  is  heated  to  200°-250°C.,  it 
is  converted  into  dextrin.  A  delicate  test  for  starch  is 
the  so-called  starch  iodide,  formed  when  the  starch  comes 
in  contact  with  iodine.  Doubt  exists  as  to  the  nature  and 
formula  of  this  characteristic  blue  compound. 

Starch  is  a  valuable  constituent  of  many  foods.  In 
laundry  work,  the  heat  of  the  iron  converts  some  of  the 
starch  into  dextrin,  which  gives  a  glossy  finish  to  the 
fibers.  Rice  starch  is  used  for  finishing  cotton  cloth  and 
is  the  chief  constituent  of  the  rice  powder  used  as  a  cos- 
metic. Wheat  starch  gives  a  paste  of  good  adhesive  quali- 
ties. Sago  is  starch  made  from  the  pith  of  certain  palm 
trees.  Tapioca  is  prepared  from  cassava,  a  starch  occur- 
ring in  the  roots  of  certain  tropical  plants.  Great  quan- 
tities of  starch  are  converted  into  dextrin  or  into  glucose. 

217.  Dextrin  has  a  light  brown  color.  Dextrin  dis- 
solves in  water,  forming  a  sticky  liquid.  This  accounts 


236  CARBON  COMPOUNDS 

for  its  use  in  adhesives  like  the  mucilage  on  the  back  of 
postage  stamps,  as  a  thickener  for  colors  in  calico  print- 
ing, and  for  tanning  extracts. 

218.  Manufacture  and  Refining  of  Sugar.  —  Several  sugars 
of  commercial  importance  were  discussed  in  connection 
with  the  production  of  grain  alcohol  (§  197).  Cane  sugar 
or  sucrose,  C^H^On,  occurs  in  sugar  cane,  sorghum,  the 
sugar  beet,  sugar  maple,  and  honey. 

The  juice  from  the  sugar  cane  is  pressed  out  by  passing 
the  cane  through  rolls,  while  it  is  obtained  from  beets  by 
cutting  them  into  small  pieces  and  extracting  with  water. 
Either  of  the  liquids  thus  obtained  is  treated  with  milk 
of  lime,  to  precipitate  the  organic  acids  and  to  separate 
the  albuminous  substances.  After  using  carbon  dioxide, 
to  precipitate  out  any  excess  of  lime,  the  liquid  is  run 
through  a  filter  press  to  take  out  the  precipitated  solids. 
The  clarified  juice  is  then  evaporated  in  vacuum  pans,  to 
get  rid  of  the  excess  of  water,  and  the  greater  part  of  the 
sugar  is  allowed  to  crystallize  out,  leaving  a  residue  of 
molasses.  The  mass  of  sugar  crystals  is  dried  by  whirl- 
ing it  in  a  centrifugal  machine.  The  product  is  brown 
sugar,  a  raw  product  which  is  generally  refined  before 
being  placed  on  the  market. 

The  raw  sugar  is  dissolved  in  water  and  filtered  through 
bone  black  in  order  to  remove  the  coloring  matters.  The 
purified  sirup  is  then  concentrated  in  vacuum  pans,  run 
out  into  tanks,  and  allowed  to  crystallize,  forming  the 
granulated  sugar  of  commerce.  The  size  of  the  crystals 
depends  upon  the  amount  of  stirring.  Although  the 
crystals  of  pure  sugar  have  a  pale  yellow  tint,  people 
demand  that  sugar  shall  be  a  pure  white.  Accordingly, 
the  sugar  refiners  add  some  blue  pigment  (ultramarine) 
to  counteract  the  yellow  color. 


ETHER  237 

Cane  sugar  melts  at  160°  C.  When  kept  at  its  melting 
point  for  a  time  and  then  allowed  to  cool,  it  solidifies  to 
a  transparent,  amber-colored  mass,  called  barley  sugar. 
When  cane  sugar  is  heated  to  210°  C.,  it  loses  water  and 
caramel  is  obtained.  This  is  much  used  as  a  coloring  and 
flavoring  material.  When  cane  sugar  is  boiled  with 
dilute  acids,  it  is  converted  into  dextrose  and  levulose, 
forms  of  sugar  which  do  not  crystallize  readily.  For  this 
reason  vinegar  is  often  added  to  candy  that  is  to  be 
pulled. 

219.  Ether,  (C2H6)2O,  is  a  representative  of  the  class 
of  alkyl  oxides.  Its  practical  importance  has  so  over- 
shadowed the  other  oxides  that  its  correct  designation  as 
ethyl  ether  is  rarely  heard. 

Ether  is  made  by  the  reaction  of  alcohol  and  concen- 
trated sulphuric  acid  heated  to  about  135°  C.  The  first 
step  is  the  formation  of  ethyl  sulphuric  acid : 

C2H5OH  4-    H2S04  — *-  C2H5HS04  +  HOH 

alcohol  sulphuric  ethyl  sulphuric          water 

acid  acid 

When  more  alcohol  is  slowly  added  and  the  above  temper- 
ature maintained,  the  second  step  occurs  : 

C2H5OH  +  C2H5HS04  — »-  (C2H5)20  +  H2SO4 

alcohol  ethyl  sulphuric  ether  sulphuric 

acid  acid 

The  sulphuric  acid  thus  regenerated  changes  more  alcohol 
into  ether  and  the  process  would  go  on  indefinitely,  if  the 
sulphuric  acid  did  not  become  too  much  diluted  by  the 
water  formed  in  the  first  reaction.  Because  it  is  made 
with  sulphuric  acid,  ethyl  ether  is  sometimes  sold  under 
the  name  of  sulphuric  ether. 
-  Ether  is  a  light,  mobile,  and  colorless  liquid,  with  a  very 


238  CARBON  COMPOUNDS 

low  boiling  point  (35°  C.).  It  dissolves  a  wide  variety 
of  organic  substances.  Water  and  ether  are  slightly 
soluble  in  each  other,  while  alcohol  and  ether  are  freely 
miscible. 

Ether  forms  very  explosive  mixtures  with  air.  Vessels 
containing  it  should  never  be  heated  over  a  gas  flame. 
The  anaesthetic  effect  of  ether  is  well  known.  It  has 
largely  replaced  chloroform  for  this  purpose,  as  its  effects 
can  be  more  readily  controlled. 

220.  Aromatic  Series.  —  Benzene  or  benzole,  C6H6,  is  the 
simplest  member  of  another  series  of  hydrocarbons,  whose 
general  formula  is  CwH2n_6-  These  hydrocarbons  are  more 
active  chemically  than  those  of  the  paraffin  series.  From 
the  benzene  hydrocarbons  are  prepared  a  wide  range  of 
carbon  compounds,  many  of  which  are  most  useful  as 
dyes,  drugs,  and  photographic  developers.  As  a  number 
of  these  organic  compounds  have  an  agreeable  and  even  a 
spicy  odor,  they  are  often  designated  as  the  aromatic  se- 
ries of  carbon  compounds.  Benzene  is  obtained  from  the 
coal  tar  of  illuminating  gas  manufacture.  It  is  a  light, 
colorless  liquid,  boiling  at  80°  C.  and  dissolves  a  wide 
range  of  carbon  compounds.  It  is  an  inflammable  liquid 
and  burns  with  a  smoky  flame.  Benzene,  C6H6,  should  not 
be  confused  with  benzine,  which  is  a  mixture  of  low  boil- 
ing paraffin  hydrocarbons,  obtained  from  petroleum. 

Like  the  paraffin  hydrocarbons,  the  aromatic  hydro- 
carbons are  the  basis  of  series  of  related  compounds  —  sub- 
stitution products,  aldehydes,  alcohols,  acids,  and  esters. 
Thus,  from  benzene  is  derived  a  phenol  or  an  aromatic 
alcohol,  C6H5OH,  more  commonly  known  as  carbolic  acid, 
because  its  hydroxyl  hydrogen  may  be  replaced  by  active 
metals  like  sodium  and  potassium,  forming  phenolates. 
It  is,  however,  one  of  the  weakest  of  acids. 


SUMMARY  239 

Carbolic  acid  is  a  white  substance,  crystallizing  in  long 
needles,  and  melting  at  43°  C.  One  part  of  carbolic  acid 
dissolves  in  15  parts  of  water,  and  the  5  %  solution  is  much 
used  for  disinfecting  purposes.  Although  one  of  the  best 
disinfectants,  it  is  now  less  used  than  formerly  as  a  sur- 
gical antiseptic.  Carbolic  acid  has  a  corrosive  action  on 
the  skin  and  mucous  membranes.  It  is  a  deadly  poison. 

The  acid  corresponding  to  benzene  is  benzoic  acid, 
CgHgCOOH.  Its  sodium  salt,  sodium  benzoate,  has  at- 
tracted wide  attention  on  account  of  its  questionable  use 
as  a  food  preservative. 

Aniline,  C6H5NH2,  is  important  as  the  parent  substance 
of  the  almost  numberless  aniline  dyes. 

SUMMARY 

Aldehydes  are  made  from  alcohols  by  the  removal  of  two  hydro- 
gen atoms  by  oxidation.  Formaldehyde,  HCHO,  is  the  simplest 
and  most  useful  aldehyde. 

Organic  Acids  are  oxidation  products  of  the  alcohols.  These 
acids  are  characterized  by  the  carboxyl  group, —COOH.  Grain 
alcohol  formed  by  fermentation  may  be  changed  by  a  second  fer- 
mentation into  acetic  acid.  Vinegar  is  a  very  dilute  solution  of 
acetic  acid  produced  by  the  fermentation  of  fruit  juices. 

Esters  or  Ethereal  Salts  are  formed  by  the  reaction  of  an  acid 
with  an  alcohol.  As  in  the  neutralization  of  an  inorganic  acid  with 
a  base,  the  other  product  is  water. 

Saponification  is  a  hydrolysis  in  which  water  splits  an  ester  into 
the  alcohol  and  the  acid  from  which  the  ester  was  formed.  Glyc- 
erin, C3H5(OH)3,  is  obtained  from  the  saponification  of  certain 
animal  fats  and  vegetable  oils.  It  is  a  by-product  in  soap  making. 

Carbohydrates  are  a_  class  of  compounds  consisting  of  carbon 
combined  with  hydrogen  and  oxygen  in  the  same  proportion  by 


240  CARBON  COMPOUNDS 

weight  as  these  two  elements  exist  in  water.     Cellulose,  sugar, 
starch,  and  dextrin  are  important  carbohydrates. 

Ethers  are  alkyl  oxides.  Ether  used  as  an  anaesthetic  is  ethyl 
oxide  (C2H5)20.  It  is  an  important  solvent  for  fats. 

Aromatic  Series  of  hydrocarbons  have  the  general  formula 
CnH2n_6.  Benzole,  C6H6,  is  the  simplest  member.  The  benzole 
hydrocarbons  yield  many  important  derivatives  valuable  as  dyes 
and  drugs.  These  are  often  spoken  of  as  coal-tar  products,  as 
many  of  them  are  made  from  the  tar  obtained  in  the  destructive 
distillation  of  coal. 

EXERCISES 

1.  How  are  aldehydes  made?    How  does  an  aldehyde  differ 
in  composition  from  an  alcohol  ? 

2.  How  does  a  copper  spiral  lamp,  burning  wood  alcohol, 
produce  formaldehyde  for  fumigation  ? 

3.  What  action  takes  place  during  the  burning  of  a  formal- 
dehyde candle  ? 

4.  What  is  formalin  ?     What  are  its  uses  ? 

5.  What  two  radicals  in  combination  constitute  an  organic 
acid  ?     Give  an  example. 

6.  Why  are  the  acids  derived  from  the  paraffin  hydrocar- 
bons often  spoken  of  as  "  fatty  acids  "  ? 

7.  What  is  meant  by  acetic  acid  fermentation  ?     Write  the 
equation.     What  is  glacial  acetic  acid  ? 

8.  Show  the  resemblances  and  differences  between  esterifica- 
tion  and  neutralization. 

9.  What  is    sapon ifi cation  ?      Write  the  equation  for  the 
saponifi cation  of  (a)  ethyl  acetate,  (6)  glyceryl  stearate. 

10.  How  does  the  hardness  of  fats  and  oils  differ  with  their 
composition  ? 

11.  Describe   briefly  two  commercial  methods  for  making 
glycerin. 


EXERCISES  241 

12.  What  happens  when  a  bottle  of  glycerin  is  left  open  to 
the  air  ? 

13.  Why  is    concentrated    sulphuric  acid   used  in  making 
nitroglycerin  ? 

14.  How  does  a  carbohydrate  differ  in  composition  from  a 
hydrocarbon  ? 

15.  What   is   pyroxylin  ?      Collodion  ?      Celluloid  ?      Gun- 
cotton  ? 

16.  Distinguish  between  dextrose  and  dextrin. 

17.  Why  should  ether  containers  be  tightly  closed? 

18.  What  is  sucrose  ?     Kock  candy  ?     Barley  sugar  ?     Car- 
amel ? 

19.  Distinguish  between  benzine  and  benzene. 

20.  What  is  a  phenol  ?     Name  an  important  one  and  give 
its  use. 


CHAPTER   XXI 
FOODS 

221.  Purposes  for  which  Food  is  needed  in  the  Body.  - 
Human  beings,  like  all  warm-blooded  animals,  need  food 
to  serve  three  distinct  purposes  in  the  body.     These  are : 

(a)  to  build  up  or  replace  worn-out  parts; 

(5).  to  act  as  a  fuel  in  keeping  the  body  warmer  than 
the  surrounding  air; 

(<?)  to  furnish  energy  to  enable  the  animal  to  do  mechan- 
ical work. 

In  the  matter  of  his  food,  an  animal  is  often  compared 
to  a  steam  engine  which  needs  fuel  to  enable  it  to  do 
mechanical  work.  But  the  analogy  is  only  partly  true, 
because  the  animal  needs  food  for  the  further  purpose  of 
repair  as  the  parts  of  his  machinery  wear  out,  and  of  keep- 
ing his  body  at  the  precise  temperature  at  wrhich  it  will 
best  do  its  work. 

222.  Fundamental  Sources  of  Food.  —  All  food  is  derived 
indirectly  from  the  carbon  dioxide  of  the  air,  together  with 
water  and  certain  soluble  salts  that  are  taken  from  the 
soil.     No  animal  is  so  constructed  that  he  can  <use  these 
substances  directly.      Plants,  however,  have  this  power, 
and  animals  obtain  their  food  by  eating  either  plants  or 
animals  that  subsist  on  vegetable  food. 

223.  Organic  Compounds.  —  Plants,  in  feeding  on  carbon 
dioxide  and  water,  build  up  in  their  bodies  many  different 
chemical  compounds.     These  are  so  numerous  and  their 

242 


CLASSIFICATION  OF  FOODS  243 

structure  is  so  complex  that  in  discussing  their  connection 
with  foods,  we  shall  refer  to  them  under  class  names,  and 
not  as  individual  compounds. 

224.  Elements  Present  in  Food  Substances.  —  The  funda- 
mental body  substance    is  protoplasm.       From  it  all  the 
tissues  of  the  organism  are  derived.     The  elements  that  it 
contains,  therefore,  represent  all  the  elements  which  must 
be  supplied  to  the  body  in  the  way  of  food.     The  chief 
elements  in  protoplasm  are :   carbon,  hydrogen,  oxygen, 
nitrogen  (these  are  the  four  elements  from  which  organic 
compounds  are  chiefly  formed),  with  phosphorus,  sulphur, 
iron,  potassium,  chlorine,  calcium,  and  a  few  others  in 
extremely  small  quantities. 

Muscle  tissue  is  composed  chiefly  of  carbon,  hydrogen, 
and  nitrogen.  Fat  is  composed  of  carbon,  hydrogen,  and 
oxygen.  The  rigid  part  of  bones  is  calcium  or  magnesium 
phosphate  and  carbonate.  Blood  contains  iron  compounds; 
the  teeth,  in  addition  to  calcium  compounds,  contain  sili- 
con and  traces  of  fluorine. 

225.  Classification  of  Foods.  —  For  the  sake  of  conven- 
ience, foods  are  divided  into  four  classes  based  on  the  dif- 
ferent purposes  they  serve  in  the  body.     As  with  most 
classifications,  however,  the  dividing  lines  are  not  sharply 
drawn,  and  a  food  that  is  set  down  in  one  class  may  serve 
the  body  in  other  ways.     The  four  classes,  the  purposes 
that  they  serve,  and  foods  typical  of  each  are  shown  below 
in  tabular  form: 

1.   Proteins. 

Composition.     Organic  compounds  very  rich  in  nitrogen. 
Purpose.  To  replace  worn-out  muscle  tissue. 

Examples.         Lean  meat,  white  of  egg. 


244  FOODS 

2.  Fats. 

Composition.     Carbon,  hydrogen,  and  oxygen. 

Purpose.  Partly  to  serve  as  fuel  in  producing  body 

heat  and  body  energy ;  they  have  a  high 
value  in  this  respect.  Partly  to  form  layers 
of  protective  tissue,  and  these  layers  also 
serve  as  a  reserve  storehouse  of  food  to  be 
drawn  on  in  case  of  necessity. 

Examples.          Butter,  meat  fat,  olive  oil. 

3.  Carbohydrates. 

Composition.     Carbon,  with  oxygen  and  hydrogen  in  the  same 

proportion  as  in  water. 
Purpose.  To  supply  body  heat  and  body  energy ;  they 

resemble  fats  in  this  respect.     Their  value 

in   this   way    is   about   half  that    of  fats. 

They   also   assist   in  building  fats  in  the 

body. 
Examples.          Starch,  cane  sugar,  and  other  sugars. 

4.  Mineral  Compounds. 

Composition.     Do  not  contain  carbon  as  a  rule. 

Purpose.  They  are  needed  in  small  quantity  to  serve  a 

great  variety  of  uses. 
Examples.        Common  salt,  the  mineral  salts  of  meat,  and 

vegetable  juices. 

226.  The  Measure  of  Food  Values.  —  Most  articles  of  food 
contain  compounds  that  represent  the  four  classes  of  food 
substances.  They  differ,  however,  very  widely  in  the 
proportion  of  protein,  carbohydrate,  and  fat  which  they 
contain.  Meat  has  no  carbohydrate,  and  many  of  the 
vegetable  foods  contain  very  little  protein.  Milk  comes 
the  nearest  of  all  food  substances  to  containing  all  the 
food  elements  in  the  proportion  in  which  they  are  needed 
in  the  body,  but  this  food  is  not  adapted  to  the  needs  of 


THE  MEASURE   OF  FOOD    VALUES 


245 


adult  life.  The  rational  diet  should,  therefore,  consist  of 
different  foods  used  in  such  proportion  that  they  meet  all 
the  needs  of  the  body. 


BREAD,  BEANS; 

*  WHITE     POTATOES     DRV 


r  PEAS,      STEAK; 

BACON      GREEN   PORTERHOUSE  LETTOCE   OYSTERS 


FIG.  80.  —  PERCENTAGE  COMPOSITION  OF  COMMON  FOODS 
W,  water  ;   C,  carbohydrates  ;  F,  fat ;  P,  protein. 

Since  fats  and  carbohydrates  serve  practically  the  same 
purpose,  that  of  supplying   the  organism  with  heat  and 


246 


FOODS 


CALORIES 

PER  LB. 

2800- 
2700- 
2600- 
2500- 
2400- 
2300- 


2200- 


2100- 
2000- 
1900- 
1800- 
1700- 


muscular  energy,  it  is  found  that  the  food  values  can  be 

considered  under  three  heads  : 
(a)  nitrogen  content, 
(6)  heat  or  energy  value, 

(<?)  the   supply  of   mineral   com- 
pounds. 

The  first  of  these  is  measured  by 
the  amount  of  protein  matter  pres- 
ent in  the  food.  The  second,  which 
is  derived  chiefly,  but  not  entirely, 
from  the  carbohydrates  and  fats,  is 
determined  by  an  instrument  known 
as  the  combustion  calorimeter.  The 
results  which  it  gives  are  expressed 
in  units  called  Calories.  A  Calorie 
is  the  amount  of  heat  necessary  to 
warm  a  kilogram  of  water  one  degree 
Centigrade.  The  number  of  Calo- 
ries furnished  by  a  given  food  in- 
dicates the  amount  of  heat  liberated 
when  it  is  completely  oxidized.  This 
is  practically  what  happens  to  food 
when  it  is  consumed  in  the  body, 
since  its  hydrogen  is  finally  con- 
verted into  water,  and  its  carbon 
into  carbon  dioxide.  The  number 
of  Calories  is  a  fair  measure  of  the 
energy  value  (Fig.  81),  because  in 

the  body,  as  in  machinery,  heat  may  be  converted   into 

mechanical  work. 


1500 
1400 
1300 
1200- 
1100- 
1000 


800 
700- 


FIG.    81.  —  CALORIFIC 
VALUE  OF  FOODS. 


227.  Quantity  of  Food  Required.  —  The  amount  and  char- 
acter of  food  needed  by  the  human  being  has  been  the 
subject  of  much  discussion,  and  authorities  are  not  in 


QUANTITY  OF  FOOD  REQUIRED  247 

complete  agreement.  In  recent  years,  however,  much 
elaborate  experimentation  has  been  carried  on  and  a  great 
deal  has  been  added  to  our  store  of  knowledge. 

Among  the  many  difficulties  that  are  encountered  in 
reaching  conclusions,  are  the  facts  that  different  human 
beings  live  and  work  under  different  conditions,  and  that 
different  bodies  work  under  different  "efficiencies."  To 
show  what  is  meant  by  this  term  we  must  use  machinery 
as  an  illustration.  A  badly  cared  for  steam  engine  will 
require  very  much  coal  to  enable  it  to  do  its  work,  while 
one  that  is  well  designed  and  kept  in  good  condition  will 
get  along  with  much  less  fuel.  Some  human  bodies  are 
not  good  machines,  and  hence  there  is  much  loss  of  energy. 

In  this  connection,  the  matter  of  digestion  is  of  much 
importance.  It  makes  little  difference  what  the  value  of 
the  food  is,  if  its  potential  energy  is  not  made  use  of  by 
good  digestion.  As  is  well  known,  the  process  of  di- 
gestion is  dependent  upon  a  great  many  factors,  a  few  of 
which  are  the  appetizing  character  of  the  food,  the  amount 
of  exercise  indulged  in  by  the  individual,  and  his  nervous 
make-up. 

It  is  also  plain  that  the  character  of  the  work  done  by  the 
individual  will  make  a  great  deal  of  difference  in  the 
amount  of  food  he  requires.  A  professional  man  who  sits 
at  his  desk  during  business  hours  will  do  far  less  mechanical 
work  than  a  laborer  who  lifts  heavy  weights  for  eight  or 
ten  hours  a  day.  The  latter,  we  would  suppose,  would 
require  considerably  more  food.  Both  ordinary  observation 
and  chemical  experiments  bear  out  this  conclusion. 

Experiments  have  also  shown  fairly  accurate  quantita- 
tive results  in  these  matters.  As  a  consequence,  we  are 
prepared  to  state  with  some  certainty  the  amount  of  food 
actually  required  by  people  who  live  under  different  con- 
ditions, and  who  perform  different  kinds  of  work. 


248  FOODS 

228.  Heat  Value  Requirement  in  Foods.  —  If  an  average- 
sized  adult  man  (160  Ib.)  did  no  mechanical  work  what- 
ever, but  sat  quietly  all  day,  he  would  require  each  day 
food  having  a  heat  value  of  from  2000  to  2100  Calories. 
This   amount   is   needed   merely   to    carry   on    the   body 
processes,  such  as  the  muscular  work  of  the   heart,  the 
movements    of   respiration,    the   work    of   digestion    and 
assimilation,  and  keeping   up  the  body  heat.     It   repre- 
sents  the  minimum  amount  of  food.     A  man  who  does 
no  mechanical  work  except  that  involved  in  going  to  his 
business,  or  in  moving  about  an  office  or  store,  needs  from 
2700  to  3000  Calories  of  food  value.     A  man  doing  light 
mechanical  work,  such  as  that  a  machinist  or  carpenter 
does,  needs  from  3000  to  3500  Calories,  and  a  man  who 
does  heavy  mechanical  work  such  as  excavating,  or  han- 
dling masonry  or  lumber  material,  will  need  from  4000  to 
6000  Calories,  depending  upon  the  amount  of  heavy  lifting 
that   he    does.     Values  for  other  conditions   of   life   are 
shown  in  the  table  on  page  253. 

229.  Protein  Requirement. — In  the   assimilation  of  the 
large  amount  of  carbohydrate  or  fat  which  the  body  needs 
to  supply  it  with  heat  and  energy,  carbon  and  hydrogen 
are  furnished  to  the  organism  as  tissue  building  material 
in   ample    quantity.     The  supply  of  these  two  elements 
need  not,  therefore,  be  separately  considered.     But   the 
case    is    different    with    the    element    nitrogen,    because 
proteins  are  needed  only  for  the  purpose  of  furnishing 
this  element  to  replace  a  certain  amount  that  is  excreted 
each  day  in  the  urine,  in  the  form  of  a  compound  known 
as  urea. 

We  get  our  protein  chiefly  from  meat,  but  it  must  be 
remembered  that  many  vegetables  also  contain  this  kind  of 
food,  sometimes  in  amounts  from  8  %  to  20  %.  The  amount 


THE  APPETITE  249 

of  protein  needed  is  a  matter  of  much  difference  of 
opinion.  The  body  has  a  rather  remarkable  power  of 
adjusting  itself  to  varying  quantities  of  this  kind  of  food, 
and  experiments  along  this  line  have  been  conducted  with 
considerable  difficulty.  In  spite  of  this  fact,  the  settle- 
ment of  the  question  is  an  important  matter,  both  because 
nitrogenous  food  is  the  most  expensive  that  we  buy,  and 
because  there  is  no  reason  for  believing  that  the  storage 
of  a  large  quantity  of  protein  matter,  or  the  extra  work 
of  its  elimination,  is  of  any  benefit  to  the  organism.  On 
the  contrary,  there  is  reason  for  believing  that  either  of 
these  conditions  is  disadvantageous. 

The  most  recent  experimenters  have  come  to  the  con- 
clusion that  a  relatively  small  quantity  of  protein  is  re- 
quired. Where  the  figure  was  formerly  put  at  100  or 
more  grams  per  day,  one  investigator  has  given  60  grams 
as  an  ample  supply  for  the  average  individual.  It  would 
appear  from  all  the  discussion  that  75  grams  (about  3 
ounces)  is  certainly  enough.  This  is  much  less  than 
most  Americans  eat.  With  such  persons  the  excess  of 
protein  is  simply  used  as  fuel,  in  the  place  of  cheaper  and 
better  carbohydrate,  and  the  kidneys  and  liver  have  the 
unnecessary  work  of  excreting  unneeded  nitrogen.  In 
cases  where  the  expense  of  food  is  a  serious  consideration, 
it  is  better  to  spend  money  for  a  sufficient  amount  of 
vegetable  food  to  furnish  the  right  amount  of  calorific 
value,  than  for  an  insufficient  quantity  of  meat  or  other 
food  that  is  rich  in  protein.  The  contrary  opinion  is 
sometimes  held. 

230.   The  Appetite  as  an  Indication  of  Food  Requirement.  — 

In  a  healthy  normal  individual,  the  appetite  is  a  fairly 
good  guide  to  the  amount  of  food  needed.  But  it  would 
be  far  from  the  truth  to  say  that  it  is  always  a  safe  indi- 


250  FOODS 

cator.  If-  the  gratification  of  the  appetite  leads  to  the 
storing  up  of  layers  of  excessive  fat,  positive  harm  is 
done,  because  there  is  interference  with  the  healthful 
operation  of  the  organism.  In  the  same  way,  many 
people  are  led  into  the  consumption  of  large  quantities  of 
protein  material  with  harmful  effects.  On  the  other 
hand,  some  people,  by  lack  of  appetite,  do  not  eat  enough 
and  their  bodies  are  weakened.  In  such  cases,  the  appetite 
is  plainly  not  a  safe  guide.  The  intelligence,  using  known 
scientific  facts,  should  be  used  in  planning  dietaries. 

231.  Mineral  Constituents  of  Food.  — Iron,  although  pres- 
ent in  the  body  in  an  extremely  small  quantity,  is  of  vital 
importance.  It  is  contained  chiefly  in  the  haemoglobin  of 
the  blood.  When  it  is  lacking,  the  individual  suffers 
from  anaemia.  Spinach,  lettuce,  and  other  green  vege- 
tables are  particularly  rich  in  iron. 

Chlorine  is  found  in  the  body  only  as  chlorides.  We 
consume  large  quantities  of  sodium  chloride,  partly  as  a 
food  and  partly  as  a  condiment.  It  serves  many  purposes 
in  the  body,  and  in  a  curious  way  makes  us  fond  of  vege- 
tables rich  in  potassium,  such  as  potatoes.  It  is  said  that 
most  people  eat  far  too  much  salt. 

Sulphur  is  a  constituent  of  most  proteins,  and  is 
supplied  to  the  body  in  ample  and  perhaps  excessive 
amounts,  in  connection  with  this  class  of  food. 

Phosphorus.  The  full  importance  of  compounds  of  this 
element  as  constituents  of  food  has  only  lately  been 
realized.  We  assimilate  phosphorus  from  some  proteins, 
from  certain  phosphorized  fats,  and  as  mineral  phosphates. 
It  has  been  found  that  there  is  more  often  a  lack  of  phos- 
phorus than  of  protein  matter  in  food,  and  that  some 
cases  of  malnutrition  have  been  due  to  this  deficiency. 
The  desirable  amount  has  been  put  as  the  equivalent  of  at 


LUNCHEONS  FOR   HIGH  SCHOOL    STUDENTS     251 

least  2.75  grams  of  phosphorus  pentoxide,  P2O6,  per  day. 
Eggs,  milk,  whole-wheat  bread  are  especially  good  sources 
of  phosphorus  compounds. 

Calcium  and  Magnesium  compounds  occur  as  phosphates 
in  the  bones,  and  in  the  form  of  various  other  compounds 
in  the  blood  and  other  fluids  of  the  body.  They  play  a 
very  important  part  in  the  action  of  the  heart.  It  is  of 
especial  importance  that  calcium  compounds  should  be 
present  in  adequate  amounts  in  the  food  of  growing  chil- 
dren. If  lacking,  arrested  development  and  other  evils 
may  result.  It  has  also  been  found  that  adults  sometimes 
suffer  from  the  lack  of  calcium  compounds.  A  study  of 
the  foods  of  American  families  shows  that  calcium  is 
deficient  in  a  majority  of  the  cases  considered.  The 
desirable  amount  is  put  as  the  equivalent  of  1  gram  of 
calcium  oxide,  CaO,  per  man  per  day. 

Potassium.  In  spite  of  the  chemical  similarity  of  sodium 
and  potassium,  the  two  elements  are  not  interchangeable 
in  the  body.  Potassium  is  found  chiefly  in  the  blood  as 
the  sulphate.  Here  it  reacts  to  a  certain  extent  with 
sodium  chloride,  forming  sodium  sulphate  and  potassium 
chloride  : 

2  NaCl  +  K2SO4  ^±  Na2SO4  +  2  KC1 

sodium  potassium  sodium          potassium 

chloride  sulphate  sulphate          chloride 

Both  of  the  resulting  compounds  are  excreted  through  the 
kidneys.  Because  of  this  action  the  use  of  common  salt 
creates  an  appetite  for  vegetables  rich  in  potassium. 

232.  Luncheons  for  High  School  Students.  —  As  observed 
by  chemistry  teachers,  these  are  often  far  from  what  they 
should  be.  The  food  selected  should  be  nutritious,  well 
"balanced,"  of  moderately  easy  digestion,  and  varied  in 
character.  Where  a  cold  lunch  must  be  eaten  (and  it  is 


252  FOODS 

not  nearly  so  important  to  have  hot  food  as  it  is  to  have 
well-selected  food),  sandwiches,  or  milk  eaten  with  bread, 
graham  crackers,  or  shredded  wheat,  make  a  good  foun- 
dation for  the  meal.  It  is  not  necessary  to  have  meat,  es- 
pecially when  this  kind  of  food  is  eaten  at  another  time 
of  day.  The  lunch  should  contain  a  considerable  quantity 
of  vegetable  food,  or  fruits,  to  furnish  plenty  of  calcium, 
phosphorus,  and  iron.  It  is  of  great  importance  that  the 
appetite  should  not  be  satisfied  with  candy  or  other  sweet 
food,  since  the  meal  would  then  be  almost  wholly  lacking 
in  protein  and  mineral  nutrients.  In  the  way  of  dessert, 
a  little  candy  or  other  sweets  may  be  allowed,  but  pies 
and  pastry  should  be  avoided.  Cocoa  or  chocolate  as 
beverages  have  actual  food  value,  but  this  is  not  true  of 
coffee,  which  is  almost  without  food  value,  and  its  stimu- 
lating effect  produces  undesirable  rather  than  desirable 
results.  Milk  chocolate,  or  milk  chocolate  with  nuts,  has 
high  food  value,  but  lacks  some  of  the  mineral  nutrients. 
It  is,  moreover,  rather  concentrated  in  form,  and  should 
be  eaten  with  other  foods. 

233.  The  Tables.  —  The  data  quoted  in  the  following 
tables  are,  by  permission  of  the  publishers,  taken  from 
"  The  Chemistry  of  Food  and  Nutrition  "  by  H.  C.  Sher- 
man, published  by  the  Macmillan  Company. 

Table  I.  shows  the  number  of  Calories  of  fuel  value 
required  at  different  ages.  The  figures  given  are  for 
persons  of  average  weight.  In  general  the  Calories  re- 
quired are  in  proportion  to  the  weight.  A  woman  or  a 
girl  needs  as  many  Calories  as  a  man  or  boy  of  the  same 
weight,  provided  she  is  equally  active. 

Table  II.  shows  the  fuel  value  per  pound  of  important 
food  substances,  and  the  per  cent  of  protein,  fat,  and 
carbohydrate  that  they  contain. 


FOOD   TABLES 


253 


Table  III.  shows  the  mineral  constituents  (calcium, 
phosphorus,  iron,  etc.)  of  important  foods  which  are  rich 
in  this  class  of  food. 

Table  IV.  shows  the  comparative  economy  of  various 
foods.  The  difference  in  the  cost  of  actual  food  value  of 
common  foods  is  seen  to  be  astonishingly  great.  The 
prices  given  in  the  table  are  approximate  ones.*  The  exist- 
ing prices  in  any  community  depend  upon  several  eco- 
nomic factors.  The  average  price  for  a  year  is  the  best  for 
calculations. 

For  more  complete  tables  see  standard  works,  and  gov- 
ernment bulletins. 

Such  tables  are  of  practical  value  in  planning  meals. 
It  should  be  remembered  that  the  appetite  is  an  even  less 
satisfactory  indicator  of  the  kind  than  of  the  quantity  of 
food  required.  A  person  eating  a  very  large  quantity  of 
meat  would  not  only  obtain  an  undesirably  large  amount 
of  nitrogenous  food,  but  also  fail  to  obtain  a  proper  sup- 
ply of  mineral  substances,  especially  calcium  and  perhaps 
phosphorus. 

TABLE  I. 


AGE,  YEARS 

WEIGHT,  POUNDS 

FOOD  REQUIREMENT  WITHOUT 
MUSCULAR  LABOR.     TOTAL  CALORIES 
PER  DAY 

1 

22 

1000 

5 

37 

1400 

10 

57 

1800 

15 

110 

2800 

20 

143 

3000 

30 

152 

2750 

40 

154 

2500 

60 

143 

2200 

80 

132 

1600 

254 


FOODS 


TABLE  II. 


FOOD 

EDIBLE 

PORTION 

Protein, 
per  cent 

Fat, 
per  cent 

Carbohy- 
drate, 
per  cent 

Fuel  value, 
per  pound, 
Calories. 

Almonds          .              ... 

21  0 

54.9 

17.3 

2940 

Apples   . 

.4 

.5 

14.2 

285 

Asparagus                           . 

1  8 

.2 

3.3 

100 

Bacon,  smoked    

105 

64.8 

2840 

Banunas                              .     . 

1  3 

6 

22.0 

447 

Beans,  dried    . 

225 

1.8 

59.6 

1565 

Beans,  string,  fresh 
Beans,  baked,  canned  .     .     . 
Beef,  corned,  average  .     .     . 
Beef  liver        .          .... 

2.3 

6.9 
15.6 
204 

.3 
2.5 
26.2 
4.5 

7.4 
19.6 

1.7 

184 
583 
1353 

584 

Beef,  roast  
Beef,  round,  lean     .... 
Beef,  sirloin  steak   .... 
Beets 

22.3 
21.3 
18.9 
2  3 

28.6 
7.9 
18.5 
.1 

7.4 

1576 
694 
1099 
180 

Bread,  graham    
Bread,  white,  homemade 
Bread,  whole-wheat     .     .     . 
Butter 

8.9 
9.1 
9.7 
1  0 

1.8 
1.6 
.9 
'85.0 

52.1 
53.3 
49.7 

1189 
1199 
1113 
3491 

Cabbage 

1.6 

.3 

5.6 

143 

Carrots 

11 

.4 

9.3 

204 

Cauliflower      
Celery                    

1.8 
1.1 

.5 
.1 

4.7 
3.3 

139 

840 

Cheese,  American    .... 
Cheese  cottage 

28.8 
209 

35.9 
1.0 

.3 
4.3 

1990 
499 

Cherries,  fresh     
Chicken,  broilers     .... 
Chocolate 

1.0 
21.5 
12  9 

.8 
2.5 

487 

16.7 
30.2 

354 
493 

2768 

Cocoa                             ... 

21.6 

28.9 

37.7 

2258 

Corn   green 

2  8 

12 

19.0 

455 

Corn  meal 

9.2 

1.9 

75.4 

1620 

Cream 

2  5 

18  5 

4.5 

883 

Dates,  dried    

21 

2.8 

78.4 

1575 

Eggs  uncooked 

134 

105 

672 

Figs,  dried       

4.3 

.3 

742 

1437 

Flour  wheat 

114 

1  0 

75  1 

1610 

Halibut  steaks    

18.6 

5.2 

550 

Ham,  smoked,  lean      .     .     . 
Hominv 

19.8 
8.3 

20.8 
.6 

79.0 

1209 
1609 

FOOD    TABLES 


255 


TABLE  II.  —  Continued 


FOOD 

EDIBLE 

PORTION 

Protein, 
per  cent 

Fat, 
per  cent 

Carbohy- 
drate, 
per  cent 

Fuel  value, 
per  pound, 
Calories. 

Lamb  chops,  broiled    . 
Lamb,  roast    . 

21.7 
19.7 

29.9 
127 

1614 

87R 

Lard,  refined  

100.0 

•      • 

408R 

Lettuce  . 

1  2 

3 

2  9 

07 

13.4 

.9 

741 

1fi9fS 

Mackerel 

187 

7  1 

R9Q 

Milk,  skirnmed    . 

3.4 

.3 

5  1 

1  «7 

Milk,  whole    
Muskmelons   . 

3.3 
.6 

4.0 

5.0 
93 

314 

180 

Mutton,  leg     

19.8 

12.4 

863 

Oatmeal 

16.1 

72 

67  5 

1811 

Olives,  green  
Oran°'es 

1.1 

.8 

27.6 

9 

11.6 
11  6 

1357 

933 

Oysters  

6.2 

1.2 

3.7 

228 

Peaches  fresh 

7 

.1 

94 

188 

Pears      
Peas,  dried 

.6 
246 

.4 
1  0 

12.7 
6°  0 

245 

161  1 

Peas,  green      .     .     .     .     .     . 
Pie,  apple   . 

7.0 
3  1 

.5 

9  8 

16.9 
49  8 

454 
1933 

Pork  chops      
Potatoes,  white,  raw     .     .     . 
Potatoes,  sweet,  raw     .     .     . 
Prunes,  dried 

16.6 
2.2 
1.8 
2  1 

30.1 
.1 

.7 

18.4 
27.4 
73  3 

1530 
378 

558 

13fi« 

Rhubarb     

.6 

7 

3  6 

105 

Rice  .     . 

80 

3 

79  0 

1fi20 

Shad,  whole    

188 

9  5 

727 

Shredded  wheat 

105 

1  4 

77  9 

1660 

Spinach,  fresh     

9  1 

.3 

32 

109 

Squash   

1  4 

5 

90 

90Q 

Strawberries   

1  0 

.6 

74 

169 

Sufifar 

1000 

1815 

9 

.4 

3.9 

104 

Turkey  . 

°1  1 

22  9 

1320 

Turnips 

1  3 

2 

8  1 

Veal,  hind  quarter  .... 
Walnuts,  California     .     .     . 
Watermelon    

20.7 
18.4 
4. 

8.3 
64.4 
.2 

13.0 

6.7 

715 

3182 
136 

Whitefish   . 

22.9 

6.5 

680 

256 


FOODS 


TABLE  III.  —  IMPORTANT  MINERAL  CONSTITUENTS  OF  FOODS 
IN  PER  CENTS  OF  THE  EDIBLE  PORTION 


FOOD 

CaO 

P205 

Fe 

014 

03 

0003 

Asparagus 

04 

09 

0010 

Bananas    . 

01 

055 

0006 

Beans,  dried  

.22 

1  14 

0070 

Beets    

03 

09 

0006 

Blueberries    .... 

045 

O9 

Bread,  white 

03 

20 

0009 

Bread,  whole-wheat    

04 

.4 

.0015 

Butter  

02 

03 

Cabbage    . 

068 

09 

0011 

.14 

1.1 

.0024 

.077 

.10 

.0008 

Cauliflower    

.17 

.14 

Celery  

10 

.10 

.0005 

Cheese  .... 

1  i 

145 

Chocolate 

14 

90 

Corn,  sweet  

.008 

.22 

.0008 

Cucumbers    

022 

.08 

Dates    . 

10 

.12 

.0030 

.093 

.37 

.0030 

Figs,  dried    

.299 

.332 

.0032 

Fish,  halibut      

.013 

.4 

.0003 

Grapefruit     ...               . 

.03 

.04 

.0004 

Grapes 

094 

.12 

.0013 

Lemons 

05 

.02 

.0006 

Lettuce     

.05 

.09 

.0010 

Meat,  beef,  lean      

.011 

.50 

.0038 

Meat,  pork,  lean     .          

.012 

.45 

M!eat  chicken 

.015 

.58 

Milk 

.168 

.215 

.00024 

Oatmeal 

13 

.872 

.0036 

.06 

.05 

.0003 

Peaches     .     .         

.01 

.047 

.0003 

Pears              .              .          

.021 

.06 

.0003 

Peas  dried                        

.14 

.91 

.0056 

Peas  fresh                        

.04 

.26 

.0016 

FOOD   TABLES 


257 


TABLE  HI.  — Continued 


FOOD 

CaO 

P2o5 

Fe 

Potatoes 

016 

140 

.0013 

.06 

.25 

.0029 

Rice  

.012 

.203 

.0009 

Spinach          .               .          .... 

09 

13 

0032 

Squash  

.02 

.08 

.0008 

Strawberries      .          .          

.05 

.064 

0009 

.020 

.059 

.0004 

Turnips 

089 

117 

0005 

Walnuts    

.108 

.77 

.0021 

Wheat,  entire  grain   

.061 

.902 

0053 

TABLE  IV. 


FOOD 

PRICE  PER  POUND 

COST  OF  3000 
CALORIES 

Flour    . 

<$0  04 

$0  08 

Oatmeal 

06 

10 

Susrar  . 

06 

10 

Potatoes    ....          . 

.01|  (  90  per  bu  ) 

14 

Bread  ...                   .     . 

06 

15 

Beans  dried 

08 

15 

Clear  fat  pork   
Potatoes   

.20 
.02J  (1.50  per  bu  ) 

.16 
24 

Bacon  

.25 

27 

Milk     . 

03  (  06  qt  ) 

28 

Shredded  wheat     .... 
Butter 

.16 
40 

.28 
33 

Milk     .     

.04  (  08  qt  ) 

37 

Olive  oil    

.55 

40 

Milk     

05  (  10  qt  ) 

46 

Almonds,  without  shell 
Round  steak,  fat  eaten  .     . 

.60 
.20 
.24  (.35  doz.) 

.60 
.88 
1.13 

Round  steak,  fat  not  eaten 

Oysters     .     . 

.20 
15  (  30  qt  ) 

1.26 
1  90 

258  FOODS 


SUMMARY 

Foods  serve  three  purposes  in  the  body :  to  act  as  fuel  in  supply- 
ing the  energy  necessary  for  muscular  work ;  to  act  as  fuel  in 
keeping  the  body  warm  ;  and  to  furnish  material  to  repair  worn-out 
or  growing  parts. 

The  Four  Classes  of  Foods  are :  fats,  carbohydrates,  proteins, 
and  mineral  compounds.  Fats  and  carbohydrates  are  the  fuels 
that  furnish  heat  and  energy,  as  well  as  the  sources  of  carbon  and 
hydrogen ;  proteins  are  needed  only  to  furnish  nitrogen  for  the 
repair  of  tissues ;  mineral  compounds  serve  a  great-  variety  of 
purposes. 

Food  requirements  may  be  expressed  in  terms  (a)  of  Calories  of 
heat  available  from  fats  and  carbohydrates  (proteins  also  furnish  a 
certain  amount  of  fuel  value),  (b)  in  grams  of  protein,  and  (c)  in 
grams  of  mineral  compounds. 

An  active  man  weighing  about  1 60  pounds  needs  a  total  of  3000 
to  3500  calories  of  fuel  value,  including  the  small  amount  that  is 
obtained  from  the  75  grams  of  protein  needed  to  supply . nitrogen. 
Small,  but  indispensable,  amounts  of  compounds  of  calcium,  mag- 
nesium, potassium,  sodium,  phosphorus,  chlorine,  sulphur,  and  iron 
are  also  needed.  Diets  made  up  too  largely  of  one  class  of  foods, 
for  example,  sugar  or  meat,  might  leave  the  body  starved  for  min- 
.eral  constituents. 

The  appetite  is  not  a  safe  guide  to  food  requirement.  Information 
concerning  the  composition  of  food  and  its  fuel  value  is  of  great 
value  in  planning  meals,  especially  where  economy  is  desirable. 


EXERCISES 

1.  What  purposes  does  food  serve  in  the  body?  From 
what  classes  of  food  does  the  body  get  its  carbon?  Its  hy- 
drogen ?  Its  nitrogen  ?  What  other  elements  are  needed  in 
the  body  ? 


EXERCISES  259 

2.  What  is  a  Calorie  ?    Why  is  the  terra  used  in  expressing 
food  values  ? 

3.  Could  a  person  live  on  starch  alone  ?     Explain. 

•    4.    Which  person  would  require  more  food,  a  tailor  or  a, 
lumberman  ?     Why  ? 

5.  Would  a  diet  consisting  altogether  of  meat  be  desirable  ? 
Explain. 

6.  Show,  by  reference  to  the  tables,  that  bread  may  truly 
be  regarded  as  the  "  staff  of  life." 

7.  Why  should  children  not  eat  large  amounts  of  candy  ? 
What  classes  of  food  would  be  lacking  ? 

8.  Why  do  people  living  in  polar  regions  consume  large 
amounts  of  fat  ? 

9.  Show   the   advantages   of    oatmeal   as   a  food.      Why 
should  it  be  thoroughly  cooked  ? 

10.  Compare  potatoes  with  oatmeal  as  a  food. 

11.  Show  the  advantages  of  cheese  as  an  article  of  food. 
What  are  its  disadvantages  ? 

12.  Calculate  from  the  tables  the  lowest  amount  of  money 
that  you  could  live  on  for  a  week  and  meet  your  food  require- 
ments.    Consider  your  age,  weight,  and  degree  of  activity. 

13.  Show  why  milk  chocolate,  or  chocolate  with  nuts,  makes 
a  good  extra  food  for  strenuous  exertion  like  mountain  climb- 
ing. 

14.  What   mineral    compounds   are   apt   to  be   lacking   in 
American  diets  ? 

15.  What  purposes  do  such  foods  as  lettuce  and  spinach 
serve  ? 

16.  Using  the  tables,  plan  three  simple,  appetizing  meals 
that  would  meet  the  food  requirements  for  a  day,  of  a  family  of 
five  adults,  all  moderately  active  people.     Give  the  weights  of 
the  various  foods  that  you  would  use. 

17.  Plan  three  vegetarian  meals  that  would  meet  your  own 
food  requirements  for  a  day.     Give  the  weights  of  the  food. 


CHAPTER  XXII 

THE  COOKING  AND  THE  ADULTERATION 
OF  FOODS 

234.  The  Cooking  of  Foods.  —  In  the  preparation  of  food, 
cooking  serves  several  purposes.     The  main  purpose,  ex- 
cept in  the   case  of  substances  containing  starch,  is  to 
secure  variety  of  flavor,  or  to  improve  the  flavor.     This 
is  a  matter  of  dietic  importance,  since  appetizing  quality 
hastens  digestion.     Hence  the  art  of  cooking  is  an  im- 
portant one,  and  the  cook  does  well  to  impart  a  fine  flavor 
to  her  preparations.     In  the  case  of  starchy  foods,  greater 
ease  of  digestion  is  secured  by  cooking,  for  the  reason 
that  the  starch  granules  are  burst  open  and  the  starch  is 
more  directly  accessible  to  the  action  of   the  digestive 
fluids.     But  most  other  foods  are  as  easily,  or  more  easily, 
digested  in  the  raw  state.     The   cooking  process,  as  a 
rule,  does  not  materially  affect  the  food  value.     Cooking 
serves  a  very  important  hygienic  purpose  by  killing  any 
disease  germs  that  may  exist  in  the  raw  food. 

235.  The  Cooking  of  Meats.  —  The  most  important  thing 
to  bear  in  mind  in  the  cooking  of  meats  is  that  protein 
matter  is  coagulated  (made  tougher,  firmer)  by  the  ap- 
plication of  heat.     Gelatinous  matter  is  also  melted  or 
dissolved  by  the  action  of  the  heat  and  by  the  action  of 
the  juices  that  are  produced.     The  principal  methods  of 
cooking  meat  are :  broiling,  baking,  stewing,  and  frying ; 
roasting  on  'a  spit  is  infrequently  used  in  this  country. 

260 


THE   COOKING   OF  MEATS  261 

Broiling  is  the  best  method  of  cooking  small  cuts  of 
meat,  such  as  steaks  and  chops.  They  are  exposed  to  the 
direct,  intense  heat  of  coals  or  hot  iron  plates  of  the  gas 
stove,  and  the  process  is  completed  in  a  short  time.  The 
high  temperature  coagulates  the  albumen  of  the  surface 
immediately,  and  the  juices  which  are  produced  during 
the  cooking  of  the  inner  portions  cannot  easily  escape. 
These  juices  are  highly  flavored  and  contain  the  mineral 
constituents.  A  properly  cooked  steak  or  chop  presents 
a  "  puffed  "  appearance  due  to  the  expanding  action  of  the 
steam  that  cannot  easily  escape  through  the  surface  mem- 
brane of  coagulated  albumen.  An  old  saying,  "  In  cook- 
ing meat,  the  larger  the  cut  the  lower  the  temperature," 
is  a  good  one ;  of  course,  this  also  implies  that  the  process 
is  longer  with  the  larger  cut.  Hence  whole  poultry  and 
roasts  are  subjected  to  the  process  of  so-called  roasting, 
which  is,  however,  really  baking.  The  lower  tempera- 
ture is  necessary  because  otherwise  the  outer  layer  would 
be  charred  before  the  inner  parts  were  heated  to  the 
cooking  temperature  (about  180°  F.).  The  roast  should 
be  put  into  a  hot  oven  to  accomplish  the  coagulation  of 
the  outer  layer,  as  in  broiling ;  the  process  should  then 
be  continued  at  a  lower  temperature.  As  the  cooking 
proceeds,  a  considerable  quantity  of  meat  juice  collects  in 
the  baking  pan,  and  the  roast  tends  to  become  dry  and 
to  lose  much  of  its  flavor.  To  counteract  this  tendency, 
the  juice  should  be  dipped  up  from  time  to  time  and  poured 
over  the  meat,  a  process  called  basting. 

Stewing  consists  of  cooking  food  in  hot  water.  Practi- 
cally, the  temperature  cannot  go  above  the  boiling  point 
(212°  F.),  and,  in  the  case  of  meats,  this  temperature  is 
not  desirable,  except  for  a  few  minutes  at  the  beginning 
of  the  operation.  A  temperature  of  about  180°  is  prefer- 
able. If  the  purpose  is  to  make  a  soup,  or  a  "  stew,"  in 


262      COOKING   AND  ADULTERATION  OF  FOODS 

which  the  broth  is  consumed  as  part  of  the  dish,  the  cook- 
ing should  begin  in  cold  water,  since  in  this  case  it  is 
desired  to  extract  the  flavor  and  nutriment  of  the  meat  as 
much  as  possible. 

Frying,  if  properly  done,  is  the  stewing  of  food  in  fat 
or  grease.  It  is  not  a  very  desirable  way  of  preparing 
meat,  because  the  protein  matter  is  too  much  coagulated 
by  the  high  temperature  of  the  heated  fat,  which  can  be- 
come much  hotter  than  boiling  water.  This  may  riot 
happen  if  the  process  is  completed  very  quickly.  A  cer- 
tain amount  of  indigestible  fat  also  clings  to  the  food. 

Roasting,  properly  speaking,  means  the  cooking  of  large 
cuts  of  meat  before  an  open  fire  on  a  spit.  Chemically 
considered,  the  process  resembles  broiling  very  closely, 
except  that  the  meat  is  not  exposed  to  so  high  a  tempera- 
ture. Both  roasting  and  broiling  may  be  described  as 
"  the  stewing  of  meats  in  their  own  juices." 

236.  Digestion  of  Foods.  —  Digestion  takes  place  by  means 
of  both  physical  and  chemical  changes.  The  physical 
processes  consist  in  the  chewing  of  the  food  and  the  in- 
voluntary movements  of  the  walls  of  the  stomach  and  the 
intestines.  These  processes  result  in  a  thorough  mixing 
of  the  food  with  digestive  fluids,  which  are  secreted  by  dif- 
ferent organs  of  the  body  and  introduced  into  the  diges- 
tive tract  at  intervals.  A  further  effect  of  the  physical 
processes  Js  the  thorough  breaking  up  of  the  food  particles, 
until  finally  they  are  in  a  practically  liquid  state.  An 
important  part  of  this  work  is  the  "emulsifying"  of  fats; 
this  means  that  they  are  broken  up  into  such  small  glob- 
ules that  they  mix  with  water  to  form  a  liquid  of  uniform 
composition  that  will  not  separate  into  layers.  In  this 
form  the  fats  can  be  directly  absorbed. 

The  chemical  changes  of  the  digestive  process  are  ac- 


ADULTERATION  IN  FOODS  263 

complished  largely  under  the  influence  of  a  class  of  sub- 
stances called  enzymes.  These  are  complicated  organic 
compounds  which  act  as  catalytic  agents,  since  they  pro- 
duce chemical  changes  in  amounts  of  food  relatively  very 
large  in  comparison  to  their  own  quantity.  Such  catalytic 
agents  are  very  numerous  in  the  body  ;  they  are  found  in 
the  saliva,  in  the  gastric,  intestinal,  and  pancreatic  juices, 
and  in  the  blood  and  muscular  tissues.  It  is  the  office  of 
these  numerous  enzymes  to  prepare  food  for  direct  absorp- 
tion by  the  blood  and  all  the  many  tissues  of  the  body. 
They  do  so  by  breaking  up  complex  molecules  into  simpler 
ones  by  the  process  of  hydrolysis.  As  a  few  examples  of 
the  work  they  accomplish,  we  may  mention : 

(a)  the  conversion  of  starch  into  maltose ; 

(6)  the  conversion  of  maltose  into  glucose ; 

(c)  the  splitting  and  oxidation  of  glucose  ; 

(cT)  the  splitting  of  fats  into  fatty  acids  and  glycerin  ; 

(e)  the  splitting  of  proteins  into  proteons,  peptones,  etc. 

237.  Adulteration  in  Foods.  — Preservatives  are  frequently 
used  in  foods.  We  may  divide  them  into  two  classes  : 
those  which  are  of  the  nature  of  condiments  or  flavors  and 
those  which  have  no  effect  on  the  flavor.  The  use  of  the 
first  class,  preservatives  like  salt,  sugar,  vinegar,  spices, 
smoke  (in  meats),  is  generally  regarded  as  permissible, 
especially  since  they  have  a  real,  immediate  value  in  stim- 
ulating digestion  through  their  pleasant  flavor.  As  ex- 
amples of  the  second  class,  whose  use  is  generally  held  to 
be  undesirable,  we  have  boric  acid,  benzoic  acid,  benzoate 
of  soda,  formaldehyde,  sulphur  dioxide,  and  salicylic  acid. 
The  presence  of  any  of  these  substances  is  easily  recog- 
nized by  simple  tests. 

Artificial  coloring  is  used  to  give  food  an  attractive 
appearance.  Various  dyes,  copper  salts,  turmeric,  and 


264      COOKING  AND  ADULTERATION  OF  FOODS 

caramel  (burnt  sugar)  are  the  substances  most  used  for 
this  purpose.  Many  of  these  are  actually  injurious,  and 
in  general  no  adequate  reason  exists  for  the  use  of  arti- 
ficial coloring  of  any  kind.  The  public,  by  giving  alto- 
gether too  much  attention  to  appearance  in  buying  food, 
is  largely  responsible  for  this  kind  of  adulteration. 

Adulteration  and  substitution.  Under  this  head,  we  may 
mention  as  substitutes  for  olive  oil  the  use  of  cottonseed  oil 
and  peanut  oil,  either  alone  or  mixed  with  olive  oil  or  with 
lard  ;  glucose  in  place  of  sugar  products ;  saccharine  as  a 
sweetener ;  starch  in  jellies  and  spices  ;  chicory  and  cereals 
in  ground  coffee.  Flavoring  extracts,  such  as  lemon  and 
vanilla,  are  often  subject  to  adulteration  with  cheaper 
extracts  of  similar  flavor,  or  with  artificially  made  essen- 
tial oils.  In  this  country  vinegar  made  from  cider  is  sup- 
posed to  be  the  standard,  but  it  may  be  made  from  alcohol 
and  water,  from  malt  or  wine,  and  improperly  sold  as  cider 
vinegar.  Flour  is  bleached  by  treatment  with  nitrogen 
peroxide  in  order  to  make  it  very  white. 

These  adulterations  are  objectionable  in  two  ways. 
Food  of  this  sort  may  be  harmful  when  eaten,  and  it  is 
certainly  a  fraud.  Articles  that  are  sold  below  a  reasonable 
cost  of  production  should  be  viewed  with  great  suspicion. 

238.  Canned  Goods.  — These  are  generally  good  in  quality 
in  this  country.  If  the  inside  of  the  can  appears  to  have 
been  acted  on  by  the  contents,  metallic  salts,  tin,  and  pos- 
sibly lead  may  be  present.  Meat  and  fish  bought  in  cans 
should  be  examined  very  carefully  for  any  signs  of  putre- 
faction, which  is  especially  dangerous  in  this  kind  of  food. 
If  gas  issues  from  the  can  when  it  is  punctured,  or  if  there 
is  any  other  sign  of  putrefaction,  the  contents  should  be 
thrown  away.  Even  cooking  does  not  counteract  the 
ptomaine  poisons  that  may  be  present. 


SUMMARY  265 

SUMMARY 

Cooking  improves  the  flavor  of  foods,  kills  the  disease  germs 
that  may  be  present,  and,  in  the  case  of  foods  containing  starch, 
increases  the  digestibility. 

In  cooking  meats,  whether  by  broiling,  baking,  or  roasting  on  a 
spit,  the  flavor  is  better  if  the  outside  layer  of  the  meat,  is  coagulated 
as  quickly  as  possible  by  high  temperature  at  the  beginning  of  the 
operation.  Large  cuts  of  meat  should  be  cooked  at  a  lower  tem- 
perature than  small  cuts.  Meats  are  best  cooked  at  a  temperature 
of  about  1 80°  F.  after  the  initial  coagulation. 

Frying  is  not  an  altogether  desirable  way  of  cooking  food. 

Starch  is  made  more  digestible  by  cooking,  because  the  cells  of 
which  it  is  composed  are  burst  open  by  the  heat,  and  the  molecules 
are  more  directly  subject  to  the  action  of  digestive  fluids. 

Digestion  takes  place  by  both  physical  and  chemical  changes. 
The  physical  processes  result  in  the  breaking  up  of  the  food  into 
small  particles.  The  chemical  processes  are  catalytic  actions 
induced  by  enzymes  that  split  up  the  food  molecules  by  hydrolysis 
into  simpler  substances.  The  presence  of  water  is  essential  to 
these  operations. 

Adulterants  are  used  in  foods  (a)  to  preserve  them  from  fer- 
mentation or  decay,  (b)  to  make  them  more  attractive  in  appear- 
ance, or  (c)  to  substitute  a  cheaper  for  an  expensive  article. 

Preservatives  commonly  used  are :  benzoate  of  soda,  benzole 
acid,  salicylic  acid,  boric  acid,  formaldehyde,  sulphur  dioxide. 
Preservatives  such  as  salt,  sugar,  vinegar,  or  spices  are  not  usually 
classed  as  adulterants. 

Colorings.  Canned  vegetables,  canned  fruits,  and  beverages  are 
sometimes  colored  with  organic  dyes,  copper  salts,  or  caramel. 
Flour  is  bleached  by  nitrogen  peroxide. 

Substitutions.  Starch,  saccharine,  and  glucose  are  substituted 
for  cane  sugar  in  preserves  and  jellies.  Olive  oil  is  adulterated 
with  other  vegetable  oils. 


266       COOKING   AND  ADULTERATION   OF  FOODS 

EXERCISES 

1.  Why    does    cooking    make    starchy    foods    easier    of 
digestion  ? 

2.  Why     should     oatmeal     be    cooked    very    long    and 
thoroughly  ? 

3.  Why  are  most  foods  cooked  before  being  eaten  ? 

4.  What  is  the  effect  of  heat  on  protein  foods  ?     Does  this 
affect  the  digestibility  in  any  way  ? 

5.  Show  how,  by  a  kind  of  process  of  survival,  the  race 
has  come  to  have  a  taste  for  cooked  food. 

6.  In  roasting  or  broiling   meats,  why  is   it  desirable  to 
begin  the  operation  at  a  high  temperature  ? 

7.  What  is  a  proper  temperature  for  finishing  the  roasting 
of  meats  ?     Why  ? 

8.  Distinguish  between  the  broiling,  baking,  and  roasting 
of  meats.     Why  is  broiling  better  than  frying  as  a  means  of 
cooking  steaks  and  chops  ? 

9.  In  making  a  soup  from  meat,  should  the  meat  be  put 
into  hot  or  into  cold  water  ?     Why  ?     Should  the  time  be  long 
or  short  ? 

10.  Why  should  food   be   thoroughly  chewed  before  it   is 
swallowed  ? 

11.  What  happens  to  food  in  the  process  of  digestion? 

12.  Name  some  common  kinds  of  food  adulteration. 

13.  What   precautions    should   be   taken   in   using   canned 
fruits  and  vegetables  ?     In  using  canned  meats  ? 

14.  Why   should   manufacturers    be   required    to   date   all 
canned  goods  ? 

15.  Name  some  adulterations  that  result  from  the  effort  to 
give  food  an  attractive  appearance. 

16.  Oleomargarine  has  good  food  value.     What  objection  is 
there  to  its  sale  as  butter  ? 


CHAPTER    XXIII 

Q 

BREAD  MAKING 

239.  Bread  as  a  Food.  —  Bread  is  so  important  a  part  of 
human  food  that  the  term  is  often  used  figuratively  to 
stand  for  all  food,  as  in  the  phrase  "  Man  shall  not  live  by 
bread  alone."     If  we  were  to  define  the  term  we'  should 
say  that  bread  means  a  form  of  food  made  from  the  flour 
of  some  grain,  as  wheat  or  rye,  in  such  a  way  that  it  has 
more  or  less  porous  structure.     This  porosity  is  essential 
to  easy  digestion,  and  it  has  meant  much  to  the  race  that 
long   ago   a  way   was   discovered   of   giving   bread   this 
quality. 

240.  Wheat  Flour.  —  Most   of  the   bread   used  in  this 
country  is  made  from  wheat  flour.     This  is  obtained  by 
crushing  the  wheat  kernel  between  steel  rollers  and  sift- 
ing the  product  to  remove  particles  of  husk.     The  finely 
divided  substance  thus  obtained  is  composed  of  starch  and 
gluten,  together  with  small  quantities  of  sugar  and  dex- 
trin.    Starch  is  a  definite  chemical  compound  whose  com- 
position may  be  represented  by  the  formula  (C6H10O5)M. 
It  belongs  to  a  class  of  substances  known  as  carbohydrates, 
and  is  useful  as  food  because  it  is  oxidized  in  the  body  pro- 
cesses, and  thus  furnishes  heat  to  the  organism.     Gluten, 
on  the  other  hand,  is  valuable  because  it  contains  nitrogen 
compounds  which  are  needed  to  build  up  muscle  tissues. 
Wheat  makes  the  best  of  grain  foods  because  it  contains 
the  highest  proportion  of  gluten. 

267 


268  BREAD  MAKING 

241.  Importance  of  Porous  Structure  in  Bread.  —  Owing  to 
the  high  proportion  of  gluten,  wheat  flour  has  a  very  ad- 
hesive quality  when   mixed   with  water.     If.  very  little 
water  is  used  we  get  a  tough,  tenacious  mass  which  we 
call  dough.     It  is  quite  apparent  that  such  a  substance 
would  be  difficult  to  digest,  if  we  remember  that  the  pro- 
cess of  digestion  is  carried  on  by  the  chemical  action  of 
fluids,  such  as  saliva  and  gastric  juice,  which  are  secreted 
in    the   body.     They  could   not   permeate   a   non-porous 
dough,  and,  moreover,  both  starch  and  gluten  are  rather 
hard  to  digest.     Hence  all  breadstuffs    are  made  porous 
or  "light"  by  some  device  or  other.     When  such   food 
is  eaten,  the  digestive  fluids  penetrate  it  easily,  as  water 
enters  a  sponge,  and  every  particle  of   the  food  is  sub- 
jected quickly  to  their  digestive  action. 

242.  Use  of  Yeast  in  making  Bread  Light.  —  The  use  of 

yeast  for  giving  a  porous  structure  to  bread  is  an  ancient 
method  that  has  never  been  improved  upon  for  making 
digestible  bread  of  excellent  quality.  Yeast  is  a  micro- 
scopic plant  (Fig.  77)  which  grows  or  multiplies  in  solu- 
tions of  sugar,  provided  nitrogen  compounds  and  certain 
salts  are  also  present.  In  its  growth  it  secretes  ferments 
which  act  catalytically  on  the  sugars  present  in  the  flour, 
causing  a  fermentation  that  yields  carbon  dioxide  and 
alcohol.  The  amount  of  sugar  that  is  subjected  to  this 
action  is  increased  by  the  fact  that  flour  contains  diastase, 
a  ferment  which  changes  part  of  the  starch  into  a  sugar: 


6H1206  -+  2  C2H6OH  +      2  CO2 

glucose  alcohol  carbon  dioxide 


When  yeast  is  put  into  dough,  and  the  mixture  is  put  in 
a  warm  place,  the  yeast  grows  and  carbon  dioxide  is  pro- 
duced. The  gas  permeates  the  dough,  but  cannot  escape 
because  of  the  tenacious  character  of  the  mass.  As  a 


BAKING    THE  BREAD  269 

result,  the  dough  "  rises,"  that  is,  it  swells  up  because 
of  the  bubbles  of  gas  that  have  been  formed  within  it. 

The  reason  that  wheat  flour  makes  the  best  bread  is 
that  the  dough  which  it  gives  is  especially  tenacious  be- 
cause of  the  high  proportion  of  gluten.  Rye  stands  next 
to  wheat  in  this  respect.  Flour  from  some  grains  will 
not  make  bread  at  all,  because  it  does  not  contain  enough 
gluten  to  make  a  plastic,  tenacious  dough. 


FIG.  82. —  DOUGH  AFTER  KNEADING.      FIG.  83.  —  LOAF  AFTER  "RISING." 

243.  Kneading  the  Dough.  —  After  the  dough  has  risen, 
the  baker  rolls  and  folds  it,  and  by  this  process  breaks  up 
the  irregularly  sized  bubbles  of  gas,  and  distributes  them 
evenly  through  the  mixture.     He  then  shapes  the  dough 
into  loaves,  and  sets  them  to  rise  again   (Fig.  82).     The 
fermentation  continues  to  go  on  because  the  yeast  is  still 
growing  and  secreting  ferments  in  the  mixture  of  flour 
and  water.     More  carbon  dioxide  is  produced  and  makes 
the  dough  rise  in  the  pan  (Fig.  83). 

244.  Baking  the  Bread.  —  The  raised  loaves  are  next  put 
into  a  hot  oven  to  bake.     The  first  action  of  the  heat  is 
to  expand  the  bubbles  of  -carbon  dioxide,  and  the  loaf  is 
made  very  porous  or  light  (Fig.  84).     The  yeast  is  killed, 
fermentation  stops,  and  at  the  same  time  the  alcohol  and 
part  of  the  water  are  vaporized  and  driven  off.     Starch  as 
it  exists  in  flour  has  an  organized,  cellular  structure,  in 
which  form  it  is  not  easily  digestible.     In  baking,  these 


270  BREAD  MAKING 

cells  are  exploded  by  the  heat  and  the  starch  is  made  more 
easily  subject  to  the  action  of  the  digestive  juices.  The 
outside  of  the  loaf  becomes  very  hot,  and  chemical  changes 
take  place  there  which  do  not  occur  on  the  inside  because 
this  never  gets  hotter  than  the  boiling  point  of  water, 
100°  C.  This  is  due  to  the  fact  that  during  the  entire 
process  of  baking,  water  is  being  continually  turned  into 
steam  inside  the  loaf.  In  the  outside  crust,  because  of  the 

greater  heat,  starch  has  been 
largely  converted  into  dextrin, 
another  carbohydrate,  and  this  in 
turn  is  partly  converted  into 
caramel.  For  this  reason  the 
crust  of  bread  has  an  entirely 
different  taste  from  the  interior 
FIG.  84.  of  the  loaf. 

245.  Other  Means  of  making  Bread  Porous.  —  A  number  of 
other  methods  have  been  tried  for  making  porous  bread. 
One  of  these  consists  in  mixing  the  dough  in  a  gas-tight 
vessel  into  which  carbon  dioxide  is  introduced  under  consid- 
erable pressure.  The  mixture  is  stirred  in  the  vessel  until 
the  compressed  carbon  dioxide  is  mingled  with  the  dough. 
The  charged  dough  is  then  allowed  to  escape  from  the  bot- 
tom of  the  vessel.  As  it  issues,  the  diminished  pressure 
allows  the  gas  to  expand,  and  the  dough,  which  has  mean- 
while been  cut  into  loaves,  "  rises."  The  baking  proceeds 
as  with  other  bread.  Made  in  this  way,  however,  bread  is 
not  so  tasty  or  digestible  as  yeast-made  bread. 

Another  method  consists  in  mixing  a  small  quantity  of 
sodium  bicarbonate  with  the  flour,  and  in  using  a  small 
quantity  of  dilute  hydrochloric  acid  in  mixing  the  dough. 
As  the  acid  and  bicarbonate  come  together,  they  react, 
forming  common  salt  and  carbon  dioxide. 


SALT-RISING  BREAD  271 


NaHCOg  +    HC1   —  »-   CO2  +  NaCl  +  H2O 

sodium          hydrochloric  carbon       sodium          water 

bicarbonate  acid  dioxide      chloride 

This  method  closely  resembles  the  use  of  baking  powder. 

246.  Adulterants  in  Bread  Making.  —  The  addition  of  a 
small  amount  of  alum  to  dough  makes  bread  of  exception- 
ally fine  appearance.     This  is  due  to  the  fact  that  alum 
increases   the   plastic  quality  which  gluten  gives  to  the 
mixture  of  flour  and  water.     It  does  no  real  good,  and  per- 
haps impairs  the  digestibility  of  the  bread.     Copper  sul- 
phate is  used  for  the    same   purpose    and    is   even   more 
objectionable.      Limewater  is  said  to  improve  the  appear- 
ance of  the  loaf  in  a  similar  way,  and  its  use  would  do  no 
harm. 

247.  Salt-rising  Bread.  —  In  some  parts  of  the  country  it 
is  the  practice   of  housewives   to  make  a  kind  of  bread 
whose  taste  is  quite  different  from  that  of  ordinary  bread. 
The  process  differs  from  that  employed  for  yeast  bread 
only  in  the  means  used  for  bringing  about  the  fermenta- 
tion.    Corn  meal  and  a  little  soda  and  salt  are  mixed  with 
hot  water  or  milk.     After  some  hours,  this  batter,  called 
"  emptyings,"  starts  to  ferment  and  carbon  dioxide  is  pro- 
duced.    Dough  is  made  as  for  ordinary  bread,  and   the 
"  empt}dngs  "  are  added  in  the  place  of  yeast.     The  fer- 
mentation continues,  and  the  loaf  becomes  porous  from  the 
production  of  carbon  dioxide. 

This  method  is  especially  interesting  because  it  has  re- 
cently been  the  subject  of  a  scientific  investigation.  As  a 
result,  salt-rising  bread  can  now  be  made  in  bakeries  on  a 
large  scale,  with  scientific  certainty  of  result,  whereas 
formerly  efforts  to  do  this  had  been  unsuccessful,  for  the 
reason  that  the  organism  causing  the  fermentation  was  not 
known,  and  the  conditions  favorable  for  its  growth  were 


272  BREAD  MAKING 

not  understood.  The  investigator  discovered  the  bacterium 
that  is  responsible  for  the  production  of  the  gas,  and  found 
that  it  gets  into  the  mixture  from  the  corn  meal,  with 
which  it  seems  to  be  always  associated.  It  grows  best 
when  milk  is  also  present,  owing  to  the  fact  that  this  sub- 
stance contains  casein.  This  experience  indicates  that  we 
may  expect  greatly  improved  knowledge  of  cookery  from 
the  application  of  scientific  method  to  its  study. 

248.  Leavened  or  "  Raised  Foods  "  other  than  Bread.  —  So 
far  we  have  been  speaking  of  bread  in  the  common  mean- 
ing of  the  term.     In  reality,  however,  such  things  as  cake, 
biscuits,  and  muffins  are  of  the  same  nature  as  bread,  since 
they  consist  mostly  of  flour,  and  are  made  porous  in  the 
process  of  cooking.     Some  device  other  than  yeast  is  gen- 
erally employed  in  order  to  save  time. 

249.  Baking  Powders.  —  The  most  important   of  other 
leavening  agents  is  the  combination  of  dry,  powdered  sub- 
stances that  will  react  chemically  in  the  presence  of  mois- 
ture to  produce  carbon  dioxide.     Such  mixtures  are  called 
baking  powders.     They  all  contain  sodium  bicarbonate, 
NaHCOo.     This  is  the  substance  from  which  the  carbon 

o 

dioxide  comes.  The  other  constituent  is  of  such  a  nature 
that  it  will  act  as  an  acid  in  the  presence  of  moisture. 
The  principal  materials  so  used  are: 

First,  potassium  acid  tartrate  (cream  of  tartar), 
KH(C4H4O6);  its  molecule  contains  one  acid  hydrogen 
atom,  and  the  action  with  sodium  bicarbonate  is: 

NaHC08  +  KH(C4H406)  — >-  KNa(C4H4O6)  +  H2O  +  CO2 

sodium  acid  potassium  sodium  potassium        water     carbon 

bicarbonate  tartrate  tartrate  dioxide 

Second,  monocalcium  phosphate,  CaH4(PO4)2 ;  its 
action  is: 


HEALTHFULNESS   OF  BAKING  POWDERS       273 
2  NaHCO3  +  CaH4(PO4)2  — >• 

sodium  monocalcium 

bicarbonate  phosphate 

CaHP04  +  NaaHP04  +  2  CO2  +  2  H2O 

calcium  hydrogen        disodium  carbon  water 

phosphate  phosphate  dioxide 

Third,  alum,  KA1(SO4)2,  or  sodium  aluminum  sul- 
phate, NaAl(SO4)2 ;  these  substances  contain  no  acid 
hydrogen,  but  when  dissolved  in  water,  they  produce  a 
very  small  quantity  of  sulphuric  acid, 

2  KA1(SO4)2  +  6  H2O  — *-  3  H2SO4  +  K2SO4  +  2A1(OH)3 

alum  water  sulphuric        potassium          aluminum 

acid  sulphate  hydroxide 

The  result  when  acting  with  sodium  bicarbonate  is, 


6  NaHCO3  +  2  KA1(SO4)2  —  >- 

sodium                        alum 
bicarbonate 

2A1(OH)3 

aluminum 
hydroxide 

+  K2S04  H 

potassium 
sulphate 

-  3  Na2SO4  H 

sodium 
sulphate 

-  6C02 

carbon 
dioxide 

250.  Healthfulness  of  Baking  Powders.  —  As  will  be  seen 
from  the  above  equations,  one  or  more  products  of  chemi- 
cal reaction  remain  in  the  food  after  baking.  Besides 
these  products,  one  of  the  constituents  of  the  original 
powder  will  also  remain,  if  the  ingredients  of  the  powder 
were  not  mixed  in  the  exact  proportion  for  complete  chem- 
ical action.  The  possibly  harmful  action  of  these  sub- 
stances has  been  the  subject  for  considerable  discussion. 
Unfortunately,  there  is  not  much  reliable  experimental 
observation  on  which  to  base  conclusions.  The  investiga- 
tions that  have  been  carried  on  have  been  for  the  most 
part  at  the  expense  of  some  manufacturing  firm  that  was 
financially  interested  in  the  result.  Consequently  there 


274  BREAD  MAKING 

has  not  been  that  freedom  from  bias  which  is  desirable  in 
scientific  work. 

More  has  been  said  against  alum  (or  sodium  aluminum 
sulphate,  NaAl(SO4)2,  which  chemically  closely  resembles 
alum)  than  any  of  the  substances  named  above  as  constit- 
uents of  baking  powders.  Nevertheless  this  substance  is 
said  to  be  present  in  a  majority  of  the  powders  that  are  on 
the  market.  Chemists  agree  in  thinking  that  alum  itself 
would  be  very  undesirable  in  food ;  but  in  making  baking 
powder,  care  is  supposed  to  be  used  so  that  the  alum  is 
mixed  with  bicarbonate  in  such  proportion  that  the  two 
will  exactly  "  balance "  during  the  baking  process.  If 
this  happens,  the  products  left  in  the  food  are  alumi- 
num hydroxide,  sodium  sulphate,  and  potassium  sulphate. 
Opinion  is  not  altogether  agreed  that  these  have  a  harm- 
ful effect.  Since  alum  powders  are  so  largely  used,  it 
is  apparent  that  no  easily  discernible  evil  effect  follows 
their  use. 

Starch  or  flour  is  usually  added  to  the  baking  powder 
mixture.  Besides  increasing  the  bulk,  this  serves  to 
dilute  the  powder  and  thus  assists  in  keeping  "it  from 
deteriorating. 

Ammonium  bicarbonate  is  sometimes  used  in  baking 
powders.  It  helps  to  make  the  dough  light  because  on 
being  heated  it  decomposes  into  gaseous  products : 

NH4HC03  •— >-  NH3  +  H20  +  CO2 

ammonium  ammonia       water        carbon 

bicarbonate  dioxide 

Tests  for  alum  and  ammonium  compounds  in  baking  pow- 
ders are  very  easily  made. 

251.  Sour  Milk  and  Soda  for  Leavening  Agents.  —  Milk 
contains  a  sugar  known  as  lactose,  C12H22O12  .  H2O.  When 


PASTRY  275 

souring  occurs,  this  substance  is  transformed  by  fermen- 
tation into  lactic  acid,  HC3H5O3  : 

C12H22011.H20-^2C6H1206; 

milk  sugar  glucose 

C6H1206  -+  2  HC3H603 

glucose  lactic  acid        » 

The  lactic  acid  thus  produced  in  sour  milk  will  react  with 
soda  (sodium  bicarbonate)  and  produce  carbon  dioxide. 
This  method  is  much  employed  in  the  household  as  a 
quick  means  of  making  muffins  or  griddle  cakes  light. 

NaHCO3  +  HC3H5O3  — »-  NaC3H5O3  +  H2O  +       CO2 

soda  lactic  acid  sodium  lactate       water       carbon  dioxide 

The  residue  of  the  milk,  consisting  mostly  of  casein  and 
albumen,  remains  in  the  food  and  adds  value  to  it.  The 
flavor  that  it  incidentally  gives  is  a  further  reason  for  using 
this  means  of  leavening. 

252.  Pastry.  —  Pie  crust  and  similar  forms  of  pastry  are 
not  leavened,  properly  speaking.  Instead,  the  flour  is  so 
treated  that  when  baked  it  readily  crumbles  into  thin 
flakes,  and  the  desired  effect  of  exposing  much  surface  to 
the  action  of  digestive  fluids  is  thus  obtained.  By  the 
housewife,  this  method  is  termed  "shortening."  Fat  in 
the  form  of  lard,  butter,  or  oil  is  mixed  with  flour  and 
water,  and  the  dough  thus  obtained  is  rolled  into  a  thin 
layer.  This  is  folded  on  itself,  rolled  again,  and  the 
process  repeated  many  times.  In  this  way,  air- is  caught 
and  retained  between  the  layers,  and  expanding  under 
the  heat  of  the  oven,  it  plays  an  important  part  in  pro- 
ducing a  flaky  crust.  Shortening  is  used  in  making  many 
forms  of  cake,  and  in  biscuits  and  crackers. 


276  BREAD  MAKING 

SUMMARY 

Flour  is  made  by  grinding  kernels  of  grain  to  a  powder  and  sift- 
ing out  the  husk.  The  chief  food  elements  are  starch,  gluten, 
and  a  small  quantity  of  sugar. 

To  make  flour  easily  digestible  it  is  necessary  to  (a)  cook  it  in 
some  manner  in  order  to  break  up  the  starch  cells,  and  (b)  to 
make  the  finished  product  porous  or  "light." 

Wheat  Flour  is  better  for  bread  making  than  that  from  other 
grains  because  it  has  a  higher  per  cent  of  gluten  ;  this  substance 
is  necessary  to  make  the  dough  coherent  and  plastic. 

The  chief  means  of  making  cake  and  bread  light  are  (a)  yeast, 
and  (b)  baking  powders.  Both  produce  small  bubbles  of  carbon 
dioxide  gas  within  the  dough.  During  the  baking  these  expand 
and  produce  the  desired  porous  character. 

Yeast  is  a  microscopic  organism  which,  during  its  growth, 
secretes  ferments  that  convert  sugar  into  carbon  dioxide  and 
alcohol. 

Baking  Powders  consist  of  sodium  bicarbonate  mixed  with  some 
solid  acid,  or  acid-forming  substance,  in  powder  form.  Cream  of 
tartar  (potassium  acid  tartrate),  calcium  acid  phosphate,  or  alum 
is  most  commonly  used  as  the  acid  constituent. 

Sour  Milk  contains  lactic  acid  and  is  used  with  sodium  bicar- 
bonate (soda)  to  make  some  kinds  of  food  light. 

Salt -rising  Bread  is  raised  by  an  organism  that  acts  somewhat 
as  yeast  does. 

"Shortening,"  that  is,  butter  or  other  fat,  makes  food  flaky 
rather  than  light,  but  serves  a  similar  purpose  in  putting  the  food 
in  such  condition  that  much  surface  is  exposed  to  the  action  of 
digestive  fluids. 

EXERCISES 

1.  Why  is  it  desirable  to  have  bread,  cake,  and  other  flour 
foods  made  light,  though  this  is  not  true  of  other  forms  of  food? 


EXERCISES  277 

2.  Why  will  not  rice  flour  make  a  good  bread  ?     What 
other  grains  besides  wheat  will  serve  for  bread  making  ? 

3.  Why  is  thorough  cooking  necessary  when  oatmeal  is 
used  as  a  breakfast  food  ? 

4.  How   is    easy   digestibility   secured   in   such   foods    as 
macaroni,  spaghetti,  etc.  ? 

5.  What  is  yeast  ?     What  is  meant  by  the  statement  that 
it  acts  indirectly  in  producing  carbon  dioxide  ?     Write  an  equa- 
tion for  the  reaction  that  produces  the  carbon  dioxide. 

6.  What  undesirable  quality  has  bread  that  has  not  been 
allowed  to  "  rise  "  sufficiently  ?     That  which  has  been  allowed 
to  "  rise  "  too  long  ?     Why  ? 

7.  Why  does  the  action  of  yeast  stop  after  the  bread  has 
been  baked  ? 

8.  What  is  baking  powder  ? 

9.  Compare  yeast  and  baking  powder  as  leavening  agents. 
Why  is  yeast  nearly  always  used  in  bread  making,  and  baking 
powder  in  cake  making  ? 

10.  Explain  how  alum  acts  as  an  acid  in  water  solution. 

11.  Give   the   formulas   of  baking   soda,  cream  of  tartar, 
glucose,  alcohol,  and  starch. 

12.  Write  an  equation  to  show  how  carbon  dioxide  is  pro- 
duced by  the  action  of  baking  powder. 

13.  Why  should  baking  powder  be  kept  in  a  tightly  closed 
tin  can  ? 

14.  Why  should  the  baking  powder  be  mixed  with  the  flour 
before  any  liquid  is  added  ? 


CHAPTER   XXIV 


MILK 

253.  Necessity  for  Purity.  —  No  article  is  more  frequently 
used  for  food  than  milk,  and  there  exists  no  food  concern- 
ing the  production  and  handling  of  which  greater  care 
should  be  exercised.     Since  milk  is  one  of  the  few  foods 
consumed  uncooked,  any  disease  germs  that  it  contains 
are  likely  to  be  in  an  active  condition  when  the  milk 
enters  the  stomach.     In  our  large  cities,  the  death  rate  of 
children  under  five  years  of  age  has  been  repeatedly  shown 
to  bear  a  direct  relation  to  the  quality  of  milk  furnished 
in  the  open  market. 

254.  Composition.  —  The  essential  constituents  of  milk 
are  water,  milk  sugar,  protein,  and  salts  (chiefly  phos- 
phates and  chlorides).     While  these  substances  are  found 
in  the  milk  of  all  mammals,  the  percentage  composition  of 
milk  varies  greatly  with  the  kind  of  animal  producing  it. 
The  composition  varies  to  a  less  degree  among  animals  of 
the  same  species  and  to  a  still  more  limited  degree  at 
different  times  in  the  case  of  the  same  animal.     The  gen- 
eral percentage  composition  of  the  milk  of  four  species  of 
mammals  has  been  given  as  follows : 


Cow 

GOAT 

HORSE 

HUMAN 

Water 

87  17 

8570 

9075 

8741 

4.88 

4.44 

5.70 

6.21 

Fat             .     .     '.     .     . 

3.69 

4.75 

1.20 

3.78 

Protein 

3.55 

4.30 

2.00 

229 

Ash  

0.71 

0.80 

0.35 

0.31 

278 


HANDLING   OF  MILK  279 

255.  Cow's  Milk.  —  The  word  milk,  when  unqualified, 
means  the  milk  of  the  cow,  which  is  practically  the  only 
kind  of  milk  that  is  an  article  of  commerce.     The  Board 
of  Health  of  New  York  City  has  ruled  that  milk  contain- 
ing more  than  88.5%  of  water,  or  less  than  3  %  of  fat,  or 
less  than  11.5  %  of  solids,  cannot  be  legally  offered  for  sale 
in  the  city.     While  many  cases  have  been  known  in  which 
the  milk  of  an  individual  cow  has  contained  more  water  or 
less  fat  and  total  solids  than  required  by  the  Board  of 
Health,  such  a  milk  would  be  considered  of  too  low  a 
grade  for  human  consumption. 

256.  Source  and  Handling  of  Milk.  —  The  source  of  milk 
demands  most  careful  attention.     Milk  drawn  from  an  un- 
healthy cow  is  unfit  for  use  as  food.     There  is  little  doubt 
that  the  drinking  of  milk  from  tuberculous  cows  has  been 
a  frequent  cause  of   tuberculosis   in   human  beings.     A 
careful  examination  of  the  physical  condition  of  the  cow 
producing  the  milk  is,  however,  no  more  essential  than  the 
prevention    of   disease   germs    entering    the   milk    after 
it  has  been  drawn  from  the  cow.     Typhoid  fever,  scarlet 
fever,    and   diphtheria  have   been    repeatedly  caused   by 
persons  drinking   milk   containing   the   germs    of    these 
diseases.     Dangerous  germs  fall  into  the  milk  at  milking 
time    from   the  uncleaned  surface  of  the    cow    or  from 
the  hands  and  clothing  of  a  milkman  who    himself  has, 
or  has  been  exposed  to,  some  contagious  disease.     Germs 
may  enter  the  milk    with   the  dust   from   hay  or   straw 
stored   on   a   loose  floor   above  the  cow   stall.      Disease 
germs   may   also   enter    the  milk  from   the    vessel    into 
which  it  is  drawn,  or  in  which  it  is  stored,  if  the  vessel  is 
washed  with  contaminated  water  or  if,  after  use,  it  is 
not  sterilized  by  boiling  water  or  by  steam.     Dangerous 
germs  are  carried  by  the  wind  and  by  insects ;  therefore, 


280  MILK 

rnilk  utensils  should  be  protected  from  these  agencies. 
The  milk  supply  of  a  large  city  has  to  be  transported 
over  long  distances,  so  that  little  of  it  reaches  the  consumer 
in  less  than  24  hours  after  production,  and  much  of  it 
must  be  kept  sweet  from  2  to  4  days.  Milk  is  an  excellent 
medium  in  which  to  grow  bacteria.  If  it  becomes  infected 
soon  after  production,  there  is  time  for  the  bacteria  to  in- 
crease to  inconceivable  numbers  before  the  milk  is  used. 
At  38°  C.  or  100°  F.  one  bacterium  will  increase  to  75,000 
in  24  hours ;  at  21°  C.  or  70°  F.  one  bacterium  will  in- 
crease to  760  in  24  hours ;  below  10°  C.  or  50°  F.  the 
bacteria  in  milk  will  increase  very  slowly.  The  Boston 
Board  of  Health  prohibits  the  sale  of  milk  which  contains 
more  than  500,000  bacteria  per  cubic  centimeter,  or  which 
is  delivered  at  a  temperature  of  more  than  50°  F. 

257.  Souring  of  Milk.  —  The  changes  that  take  place  in 
milk  on  standing  are  chiefly  due  to  low  forms  of  life  which 
multiply   with   enormous   rapidity   in   milk.     The    most 
noticeable  change  that  takes  place  is  the  souring  of  the 
milk.     This  is  owing  to  forms  of  bacteria,  known  as  the 
lactic  acid  bacteria,  that  enter  the  milk  and  rapidly  mul- 
tiply in  it.     They  convert  the  milk  sugar,  which  is  sweet, 
into   lactic   acid,  which   is   sour.      The   lactic  acid  soon 
accumulates  to  a  quantity  sufficient  to  cause  one  of  the 
proteins,  casein,  to  separate,  leaving  behind  a  thin  liquid 
called  whey.     In  other  words,  the  lactic  acid  causes  the 
milk  to  curdle. 

258.  Putrefaction  of  Milk.  —  At  the  same  time  the  lactic 
acid  fermentation  is  going  on  in  the  milk,  putrefactive 
bacteria  are  at  work.     While  at  first  they  work  less  rapidly 
than  the  lactic  acid  bacteria,  they  soon  cause  some  of  the 
casein  to  decompose,  thus  producing  poisonous  substances, 
ptomaine  poisons.     Such  milk  is  absolutely  unfit  for  food. 


KEEPING   OF  MILK  281 

The  putrefactive  bacteria  are  less  easily  killed  by  heat 
than  the  lactic  acid  bacteria. 

259.  Methods  of  Keeping  Milk  Sweet.  —  Since  the  forms  of 
bacteria  that  cause  milk  to  sour  are  present  in  large  num- 
bers in  the  air,  it  is  not  possible  to  keep  sweet  for  more 
than  a  day  or  two  pure  milk  that  is  exposed  to  the  air  at 
ordinar}'  temperature.     In  order  to  have  pure  milk  remain 
sweet  for  several  days,  the  utmost  care  must  be  taken  to 
protect  it  from  dust  and  from  filth  of  every  description 
and,  moreover,  it  must  be  kept  at  a  temperature  little 
above  the  freezing  point,  so  that  the  bacteria  which  un- 
avoidably enter  the  milk  will  multiply  very  slowly.     All 
this  adds  greatly  to  the  expense  of  handling  the  milk  and 
puts  the  price  beyond  what  the  average  citizen  can  afford 
to  pay. 

Two  methods  that  do  not  add  materially  to  the  selling 
price  have  been  extensively  employed  to  increase  the  time 
milk  will  keep  sweet.  One  of  these  is  to  add  some  chemi- 
cal as  a  preservative,  and  the  other  is  pasteurization. 

260.  Preservatives.  —  The  preservatives  that  have  been 
most  extensively  employed  in  milk  are  formaldehyde,  boric 
acid,  and  borax.     These  are  objectionable  on  account  of 
their  poisonous  properties.     Although  they  are  generally 
added  to  milk  in  very  small  quantities,  especially  in  the 
case  of  formaldehyde,  they  should  never  be  used.     Par- 
ticular care  should  be  exercised  to  see  that  they  are  kept 
out  of  milk  for  infants.     Sodium  bicarbonate  has  recently 
come  into  use  as  a  preservative. 

261.  Pasteurized  Milk.  —  True  pasteurization  of  milk  con- 
sists in  heating  it  to  a  temperature  of  from  145°  F.  (63°  C.) 
to  167°  F.  (75°  C.),  keeping  the  milk  from  20  to  40  minutes 
between  the  temperatures  mentioned,  then  rapidly  cooling 


282 


MILK 


the  milk  and  keeping  it  at  a  low  temperature  until  delivered 
to  the  consumer.    Milk  that  has  been  held  at  the  temperature 

mentioned  for  less  than  a  minute 
has  so  frequently  been  sold  as 
pasteurized  that  Boards  oJ 
Health  are  beginning  to  demand 
that  the  milk,  after  being  raised 
to  the  required  temperature  ir 
the  pasteurizing  machine,  shal 
be  run  into  a  holding  machine 
One  form  of  holding  machine 
is  made  up  of  compartment* 
which  revolve  slowly  and  are  sc 
arranged  that  milk  entering  one 
compartment  is  kept  at  a  tem- 
perature of  at  least  140°  F.  foi 
20  minutes  before  it  can  be  de- 
FIG.  SS.-WILLMANN  REGENER-  Hvered  to  the  cooling  apparatus 

Milk  that  has  been  improp- 

erly  pasteurized  may  keep  sweet  for  a  considerable  period 
of  time  and  yet  be  then 
more  dangerous  to  use 
than  raw  milk.  The 
lactic  acid  bacteria  are 
quite  readily  killed  by  a 
short  exposure  to  a  tem- 
perature of  160°  F.,  while 
spore-bearing  putrefac- 
tive bacteria  are  little 
affected.  The  customer, 
depending  on  the  sweet- 
ness of  the  milk  as  an 
indication  of  its  purity,  fails  to  realize  that  it  may  contain 
putrefactive  bacteria  and  the  poisons  produced  by  them. 


FIG.  86. — WILLMANN  REGENERATIVE 
PASTEURIZER  TAKEN  APART. 


MODIFIED   MILK  283 

The  consumer  should  realize  that  at  best  pasteurized  milk 
is  not-  sterilized  milk.  Since  it  is  not  entirely  free  from 
undesirable  germs,  it  should  be  kept  at  as  low  a  tempera- 
ture as  is  necessary  for  preventing  the  rapid  growth  of 
bacteria,  or  better  still,  it  should  be  consumed  within  a 
few  hours  after  pasteurization. 

It  is  fortunate  that  the  disease-producing  gernls  generally 
found  in  milk  are  not  spore-bearing  and  are  killed  by  the 
temperature  used  in  pasteurization.  There  is  no  doubt 
that  a  milk  carefully  pasteurized  and  kept  cool  until 
needed,  is  far  safer  than  ordinary  raw  milk. 

262.  Certified  Milk.  —  Milk  commissions  have  been  formed 
in  various  parts  of  the  country  to  formulate  and  enforce 
rules  governing  the  production  and  handling  of  a  portion 
of  the  milk  to  be  placed  on  the  market.     Milk  dealers 
have  a  right  to  label  their  milk  as  being  certified  by  a 
milk  commission  when  the  commission  grants  them  that 
privilege.     This  is  done  only  after  a  thorough  inspection 
has  been  made  of  the  herd  of  cows  producing  the  milk,  of 
the  water  supply  of  the  dairies,  and  of  all  utensils  used  in 
handling  the  milk.     The  rigid  enforcement  of  the  rules 
governing  the  production  and  handling  of  certified  milk 
insures  to  the  purchaser  a  clean,  pure  milk  from  a  healthy 
cow.      A  certified  milk  is  likely  to  be  of  unimpeachable 
quality  only  when  the  milk  commission  is  composed  of 
upright,  energetic  men  who  are  untiring  in  their  efforts  to 
have  the  rules  of  the  commission  enforced.     It  shooild  be 
remembered,  however,  that  it  is  the  method  of  production 
and  not  the  milk  that  is  certified. 

263.  Modified  Milk.  —  If  an  infant  is  to  be  fed  on  cow's 
milk,  it  is  essential  not  only  to  have  the  milk  pure  and 
sweet  but,  in  addition,  its  composition  should  be  changed 
so  as  to  have  it  resemble  mother's  milk  as  closely  as  possible. 


284 


MILK 


FIG.  87.  —  REGENERATIVE  PASTEURIZER,  SECTION  THROUGH  Axis. 

The  cold  milk  is  led  into  the  feed  tank  of  the  Willmann  pasteurizer  (Fig.  87)  from 
which  it  is  equally  distributed  into  the  troughs  1-1,  whence  it  is  distributed  over  the  cor- 
rugated surfaces  2-2-2-2,  through  small  perforations,  as  indicated  by  the  arrows  3-3-3-3, 
and  flows  by  gravity  over  the  corrugated  surfaces  as  indicated  by  the  arrows  4-4-4-4 
until  it  reaches  the  bottom  of  the  corrugated  section,  when  it  passes  through  the  openings, 
indicated  by  the  arrows  6-6,  into  the  space  7-7.  Its  course  is  then  turned  upwards,  as 
shown  by  the  arrows  8-8,  into  the  space  between  the  plates  9-9-9-9,  where  the  temper- 
ature is  raised  to  145°  F.,  and  the  milk  is  thrown  out  into  the  pipe  10  by  the  revolving 
agitator  11-11-11-11.  From  this  pipe  1 0  the  milk  is  led  into  the  holding  machine-  The  . 
valve  12  is  a  3-way  valve  which  can  be  turned  so  that  the  milk  will  be  carried  to  the  hold- 
ing machine,  or  into  the  pipe  1 3  Pipe  1 3  is  used  when  no  holding  machine  is  employed 
and  when  the  machine  is  first  started,  until  the  temperature  of  the  first  milk  is  raised  to 
145°  F.  The  hot  milk  from  the  holding  machine  is  brought  back  through  the  valve  14  to 
the  pipe  1 3  which  leads  to  the  bottom  of  the  corrugated  section  and  connects  to  the  space 
between  the  corrugated  sections  at  1 5.  The  hot  milk  flows  as  shown  by  the  arrows  16-16 


EVAPORATED  MILK 


285 


Before  such  a  change  can  be  made  intelligently,  it  is  neces- 
sary that  the  composition  of  the  milk  to  be  modified  should 
be  determined,  that  is,  the  milk  must  be  analyzed.  This 

should  be  done  only  by 
a  trained  milk  chemist. 


SWEETENED 

CONDENSED 

MILK 


264.  Sterilized    Milk 
contains  no  living  or- 
ganisms.    The  killing 
of    the   germs   in   the 
raw  milk  removes  the 
danger      that      might 
arise  from  taking  into 
the  system  disease-pro- 
ducing bacteria.    Ster- 
ilization   is    generally 
accomplished  by  boil- 
ing  the    milk.      This 
will  not  kill  the  spores 
of  bacteria,  and  hence 
the  milk  must  be   al- 
lowed to  cool  so  that 
any    spores    which    it 
contains  may  start   to 
grow.    Then  it  should 
be  heated  again. 

265.  Evaporated  Milk 

is  milk  that  has  been 
concentrated  until  it 
contains  not  less  than  28%  of  milk  solids  of  which  7.7% 
is  milk  fat.  It  is  unsweetened  and  is  sold  in  sealed 

through  15  and  then  upward  between  the  corrugations,  as  indicated  by  the  arrows  17-17, 
and  out  through  the  pipe  18.  The  hot  milk  is  thus  cooled  and  the  cold  milk  heated. 
Valve  20  is  for  driving  the  hot  milk  from  the  space  between  the  corrugations. 

The  final  heating  is  accomplished  by  hot  water  in  the  space  19-19  against  the  surfaces 
9-9,  and  the  final  cooling  by  a  cooler  separate  from  the  pasteurizer. 


FIG.  88.  —  PERCENTAGE  COMPOSITION  OF 
MILK. 


286  MILK 

cans.  In  the  production  of  any  form  of  condensed  milk, 
the  greatest  care  has  to  be  exercised  to  obtain  a  high  quality 
of  raw  milk,  if  an  attractive  article  is  to  be  manufactured. 
The  evaporation  is  carried  on  in  vacuum  pans  so  that  the 
milk  is  not  heated  to  a  sufficiently  high  degree  to  impart 
to  it  a  cooked  flavor.  It  is  then  commonly  put  through  a 
homogenizer  (§  269)  to  prevent  the  separation  of  fat. 
After  being  sealed  in  cans,  the  evaporated  milk  is  sterilized 
by  exposing  the  cans  to  superheated  steam  ranging  in 
temperature  from  226°  F.  to  245°  F.  Either  while  the 
evaporation  is  in  progress,  or  later  in  the  process,  the  cans 
are  shaken  to  convert  their  contents  into  a  smooth  product. 

266.  Sweetened  Condensed  Milk  is  required  to  contain  at 
least  as  large  a  percentage  of  milk  sugar  and  milk  solids 
as  evaporated  milk.     In  place  of   sterilization,  sufficient 
cane  sugar  is  added  to  prevent  fermentation.     The  amount 
of  cane  sugar  used  is  about  40  %  of  the  product  (Fig.  88). 
Unsweetened  condensed  milk  is  superheated  in  the  vacuum 
pan  by  blowing  live  steam  into  it. 

267.  Advantages  of  Condensed  Milks.  —  A  high  grade  of 
raw  milk  is  taken  to  start  with,  and  the  natural  milk  solids 
and  fat  are  retained  in  the  condensed  milk,  while  the  volume 
of  the  milk  is  greatly  reduced,  and  the  cost  of  transporta- 
tion correspondingly  lessened.     Both  evaporated  milk  and 
sweetened  condensed  milk  can  be  kept  for  ma*ny  months 
without  undergoing  appreciable  change.     They  may  conse- 
quently be  prepared  in  remote  rural  districts  where  milk 
is  cheap,  and  be  transported  to  cities  where  the  demand  for 
milk  is  great.     By  the  addition  of  water,  evaporated  milk 
of  good  quality  may  be  converted  into   a  product   that 
is  superior  to  the  poorer  grades  of  milk  often  sold  in  large 
cities.     These  facts  are  causing  condensed  milk  to  be  used 
in  increasing  quantities. 


HOMOGENIZED  MILK  287 

268.  Powdered  Milk.  —  Many  attempts  have  been  made 
to  remove  practically  all  of  the  water  from  milk,  and  reduce 
the  total  milk  solids  to  a  powder.     Some  of  these  have 
been  so  successful  that  several  brands  of  powdered  milk 
are  at  present  on  the  market.     One  of  the  most  ingenious 
methods  employed  consists  of  first  condensing  the  milk 
in  a  vacuum  pan,  and  then  spraying  the  still  -fluid  milk 
under  high  pressure  through  fine  nozzles  into  an  inclosed 
room,  and  against  a  current  of  hot  air.     It  has  been  esti- 
mated that  one  pint  of  milk  in  the  form  of  the  spray  presents 
about  two  acres  of  surface.     The  moisture  still  remaining 
in  the  milk  is  almost  instantly  absorbed  by  the  hot  air  and 
the  milk  solids  fall.     When  whole  milk  is  used,  the  milk 
powder  obtained  from  it  has  good  keeping  properties,  and 
Avhen  skimmed  milk  is  employed,  the  powder  will  keep 
still  better.     The  milk  obtained  by  the  addition  of  water 
to  powdered  milk  is  wholesome  and  of  fair  qualit}r.     It  is 
excellent  for  use  in  cooking.     Powdered  milk  when  dis- 
solved in  water  furnishes  an  ideal  medium  for  the  culture 
of  lactic  acid  bacteria,  as  it  is  thoroughly  sterilized  and 
can  be  inoculated  with  pure  cultures. 

269.  Homogenized   Milk  is   milk   that   has   been  forced 
through  minute   openings  under   a  tremendous   pressure 
reaching  approximately  from  1500  to  3000  pounds  to  the 
square  inch.     The  fat  globules  are  broken  and  evenly  dis- 
tributed through  the  milk  so  that  an  excellent  emulsion  is 
obtained  from  which  the  fat  does  not  separate  readily. 
It  is  possible  to  incorporate  sweet  butter  with  skimmed 
milk,  or  powdered  milk,  by  the  process  of  homogenization. 
Homogenized  milk  is  always  thicker  than  the  milk  from 
which  it  was  made,  and  appears  to  contain  more  fat  than  is 
actually  the  case.     It  has  been  sold  by  dairymen  as  cream. 
While  homogenized  milk  furnishes  a  pleasing  article  to 


288  MILK 

use  in  tea  or  coffee,  it  is  impossible  to  convert  it  into 
whipped  cream.  It  is  fraudulent  to  sell  homogenized 
milk  as  cream.  Ice  cream  manufacturers  use  homogenized 
milk  in  large  quantities. 

270.  Fermented  Milks  of  various  kinds  have  been  highly 
esteemed  for  centuries  by  people  of  different  nationalities. 
In  this  country,  buttermilk  has  long  been  considered  a 
health-producing  and,  by  many,  a  delicious  drink.  Butter- 
milk is  that  portion  of  the  cream  that  is  left  after  the 
removal  of  nearly  all  of  the  milk  fat  during  the  process  of 
churning.  As  the  cream  is  generally  permitted  to  sour 
before  being  churned,  the  buttermilk  contains  a  small 
amount  of  lactic  acid.  The  wholesome  qualities  of  butter- 
milk are  thought  to  be  due  chiefly  to  lactic  acid  bacteria. 

Within  recent  years  a  considerable  number  of  brands 
of  fermented  milks  and  of  cultures  for  their  production 
have  been  placed  on  the  market  under  such  names  as 
Zoolak,  Lacto-Bacilline,  Vitallac,  Kumiss,  Fermilac,  etc. 
These  preparations  have  come  to  be  well  thought  of  as 
correctives  for  intestinal  disorders.  As  it  is  difficult  in 
our  large  cities  to  obtain  a  satisfactory  buttermilk,  tablets 
and  capsule  cultures  for  the  preparation  of  artificial  butter- 
milk from  sweet  milk  have  become  articles  of  commerce. 
These  contain  more  or  less  pure  cultures  of  lactic  acid  pro- 
ducing bacteria  and  are  accompanied  by  directions  for  the 
preparation  of  a  fermented  milk.  After  the  milk  has  been 
pasteurized  at  a  high  temperature,  it  is  inoculated,  and  is 
then  kept  at  a  temperature  suitable  for  the  growth  of  the 
bacteria  used,  until  the  desired  degree  of  acidity  has  been 
attained.  The  process  is  then  stopped  by  lowering  the 
temperature  of  the  product  to  a  point  below  that  at  which 
the  bacteria  grow.  The  ordinary  lactic  acid  producing 
bacteria  are  likely  to  cause  the  casein  of  the  milk  to  pre- 


SUMMARY  289 

cipitate  and  settle,  leaving  on  top  a  clear  liquid,  the  whey. 
Most  of  the  fermented  milk  on  the  market  is  made  from 
skimmed  milk. 

Recently  'cultures  of  Bacillus  bulgaricus,  for  use  in 
bringing  about  lactic  acid  fermentation  in  milk,  have  been 
placed  on  the  market.  This  ferment  differs  in  several 
respects  from  the  ordinary  lactic  acid  bacteria.  It  does 
not  cause  the  casein  to  separate  from  the  whey ;  it  pro- 
duces a  higher  percentage  of  lactic  acid  and  thrives  at  a 
higher  temperature  than  the  ordinary  lactic  acid  bacteria. 
A  temperature  of  100°  F.  is  best  adapted  to  the  growth  of 
Bacillus  bulgaricus  and  the  lower  temperature  of  70°  F.  is 
best  for  the  growth  of  the  ordinary  lactic  acid  bacteria. 
The  Bacillus  bulgaricus  also  survives  the  digestive  opera- 
tions of  the  stomach  and  is  carried  into  the  intestines, 
where  it  continues  to  produce  lactic  acid.  Both  for  this 
reason  and  because  it  thrives  well  at  the  body  temperature, 
the  bulgaricus  is  considered  the  best  lactic  acid  bacillus  for 
making  sour  milk  preparations. 

Kumiss  probably  originated  in  Asia,  where  the  term 
was  applied  to  fermented  mare's  milk.  In  this  country,  a 
fermented  milk  sold  as  Kumiss  is  made  from  cow's  milk. 
The  best  results  are  said  to  be  obtained  by  bringing  about 
an  alcoholic  fermentation  in  a  good  quality  of  buttermilk 
to  which  cane  sugar  has  been  added.  Yeast  is  used  to 
ferment  the  sugar,  causing  the  production  of  alcohol  and 
carbon  dioxide.  The  carbon  dioxide  imparts  to  the  Kumiss 
the  sharp  taste  of  a  plain  soda  and  produces  a  desirable 
effervescence. 

SUMMARY 

Milk  is  such  a  common  article  of  diet  that  its  purity  is  essen- 
tial to  the  health  of  the  community.  The  disease  germs  that 
milk  contains  are  not  likely  to  be  killed  before  the  milk  is  used. 


290  MILK 

Typhoid  fever,  scarlet  fever,  and  diphtheria  are  some  of  the 
forms  of  disease  that  are  known  to  be  occasioned  by  the  use  of 
infected  milk. 

The  Bacterial  Content  of  milk  increases  with  tremendous  rapidity 
between  80°  F.  and  100°  F.  Below  50°  F.  there  is  practically  no 
increase  in  the  number  of  bacteria  present. 

Souring  of  milk  is  brought  about  by  forms  of  bacteria  that  convert 
milk  sugar  into  lactic  acid.  The  growth  of  Putrefactive  Bacteria 
that  produce  dangerous  poisons  (ptomaines)  in  milk  is  held  in 
check  by  bacteria  that  form  lactic  acid.  Many  of  the  putrefac- 
tive bacteria  produce  spores  that  are  not  readily  killed  by  heat. 

Preservatives  in  the  form  of  deleterious  chemicals,  such  as 
formaldehyde  and  borax,  should  never  be  used  to  keep  milk  sweet. 

Pasteurization  of  milk  consists  in  heating  milk  to  a  temperature 
of  from  145°  F.  to  167°  F. ,  holding  it  between  these  temperatures 
for  20  minutes,  and  then  quickly  cooling  it.  Nearly  all  the  bacteria 
that  produce  diseases  are  killed  by  this  treatment,  but  the  milk  is 
not  sterilized.  Pasteurized  milk  should  be  kept  at  a  tempera- 
ture between  40°  F.  and  50°  F.  until  needed  for  use. 

Certified  Milk  is  supposedly  produced  according  to  rules  formu- 
lated and  enforced  by  a  milk  commission.  The  label  "  certified  " 
depends  for  its  value  upon  the  integrity  of  the  milk  com- 
missioners. 

Modified  Milk  is  cow's  milk,  the  composition  of  which  has  been 
changed  to  make  it  more  closely  resemble  mother's  milk.  The 
change  should  be  based  upon  analyses  made  by  a  competent  milk 
chemist. 

Sterilized  Milk  is  free  from  living  organisms.  It  is  prepared 
by  treating  raw  milk  so  as  to  destroy  all  bacteria  and  their  spores. 
Such  milk  will  remain  sterile  if  not  permitted  to  come  in  contact 
with  air,  or  if  it  contains  some  poison  which  will  kill  any  germs 
that  may  reach  it. 

Evaporated  Milk  differs  from  Sweetened  Condensed  Milk  in  that 
no  sugar  is  added  to  the  former  during  its  preparation.  Both 


EXERCISES  291 

are  prepared  by  evaporating  the  water  from  milk  until  the  residue 
has  the  consistency  of  thick  cream. 

Powdered  Milk  is  produced  by  removing  the  water  from  raw  milk 
and  converting  the  milk  solids  into  a  powder. 

Homogenized  Milk  is  made  by  the  use  of  enormous  pressure  to 
force  raw  milk  through  minute  openings.  The  process  breaks  the 
fat  globules  and  thickens  the  milk. 

Fermented  Milks  are  produced  by  inoculating  raw  milk  with 
forms  of  bacteria  believed  to  produce  changes  which  make  the 
product  more  wholesome  than  ordinary  milk. 


EXERCISES 

1.  Why  is  a  bountiful  supply  of  pure  milk  essential  to  the 
health  of  the  community  ? 

2.  Compare  the  average  composition  of  cow's  milk  with 
mother's  milk. 

3.  What  is  the  highest  content  of  water,  the  lowest  con- 
tent of  fat  and  total  solids  permitted  in  milk  legally  offered 
for  sale  in  New  York  City  ? 

4.  Briefly  tell  about  some  of  the  ways  in  which  disease 
germs  enter  milk. 

5.  Why  is  it  desirable  that  milk  carried  from  the  country 
to  large  cities  should  be  kept  at  a  temperature  between  40°  F. 
and  50°  F.  while  in  transit  ? 

6.  What  causes  milk  to  sour  ? 

7.  What  are  some  of  the  methods  employed  to  keep  milk 
sweet  ? 

8.  Which  of  the  methods  employed  to  keep  milk  sweet  is 
the  most  desirable  ? 

9.  Is  a  sweet  milk  always  a  safe  milk  to  use  ?     Explain. 

10.  What  are  the  advantages  of  pasteurized  milk  ? 

11.  How  does  pasteurized  milk  differ  from  sterilized  milk  ? 


292  MILK 

12.  Why  is  it  essential  that  pasteurized  milk  be  kept  cool 
until  required  for  use  ? 

13.  Under  what  conditions  may  pasteurized  milk  be  more 
dangerous  to  use  than  raw  milk  ? 

14.  What  is  certified  milk  ? 

15.  Does  the  fact  that  a  milk  is  certified  necessarily  mean 
that  the  milk  is  safe  to  use  ? 

16.  What  is  modified  milk  ? 

17.  Why  is  it  impossible  to  give  definite  general  directions 
for  the  correct  modification  of  cow's  milk  ? 

18.  Distinguish   between   evaporated   milk  and  sweetened 
condensed  milk. 

19.  What  is  powdered  milk  ? 

20.  How  is  milk  homogenized  ? 

21.  How  does  homogenized  milk  differ  from  cream  when 
whipped  ? 

22.  Mention  some  of  the  names  given  to  fermented  milks. 

23.  What  advantage  is  there  in  the  use  of  Bacillus  bulga- 
ricus  instead  of  the  ordinary  lactic  acid  bacteria  ? 

24.  Why  is  Kumiss  effervescent  ? 


CHAPTER  XXV 

CREAM,  ICE  CREAM,  BUTTER,  AND  CHEESE 

271.  Cream.  —  Milk  is  a  solution  that  contains  in  sus- 
pension globules  of  fat  and  also  particles  of  casein  which 
are  in  chemical  combination  with  calcium.  When  fresh 
milk  is  allowed  to  stand  for  some  time,  the  fat  globules 
gradually  rise  to  the  top  of  the  milk  and  form  a  layer 
rich  in  fat.  This  layer  is  the  cream.  As  the  process  of 
obtaining  cream  by  allowing  the  milk  to  stand  is  too  slow 
for  the  modern  dairy,  separators  are  generally  used  to 
separate  the  cream  from  the  remaining  portions  of  the 
milk.  A  separator  is  a  centrifugal  machine  in  which  the 
milk  is  made  to  rotate  rapidly.  The  cream,  being  the 
lighter  portion  of  the  milk,  collects  near  the  axis  of  rota- 
tion, while  the  heavier  portions  are  thrown  toward  the 
circumference.  Cream  should  contain  at  least  18%  of 

fat. 

When  cream  is  beaten  with  some  implement,  such  as  an 
egg  beater,  the  clusters  of  fat  globules  are  broken  and, 
before  the  fat  collects  in  the  form  of  butter,  the  cream 
thickens  so  that  the  particles  of  air  which  become  en- 
tangled are  held,  producing  a  foam  which  is  known  as 
whipped  cream.  Cream  that  has  been  recently  heated  does 
not  whip  readily.  The  viscosity  may  be  restored  to  such 
a  cream  by  allowing  it  to  remain  in  a  cool  place  for  a  few 
hours,  or  by  the  addition  of  a  solution  known  as  "  Vis- 
cogen."  This  is  prepared  by  slaking  1  part  of  lime  in  3 
parts  of  water  and  adding  to  the  slaked  lime  2J  parts  of 
sugar  dissolved  in  5  parts  of  water.  The  mixture  i§ 

293 


294      CREAM,  ICE  CREAM,   BUTTER,   AND   CHEESE 

shaken  at  intervals  during  2  or  3  hours,  after  which  it  is 
allowed  to  settle  and  the  clear  liquid  is  siphoned  off. 
From  1%  to  1J%  of  "Viscogen"  is  added  to  the  cream. 
Cream  should  be  at  a  low  temperature  (40°  F.  to  50°  F.) 
when  whipped. 

272.  Ice  Cream  is  popularly  supposed  to  be  a  frozen  mix- 
ture of  cream,  sugar,  and  flavoring  material,  to  which  may 
have  been  added  some  artificial  color.  As  a  matter  of 
fact,  it  often  differs  widely  from  such  a  mixture.  In 
addition  to  the  articles  mentioned,  several  other  sub- 
stances are  commonly  used  in  making  ice  cream.  Eggs 
and  a  considerable  portion  of  milk  are  often  used  in  the 
homemade  article.  Such  a  product  is  really  a  frozen 
custard.  Gelatin  is  in  many  instances  added  to  give 
firmness,  so  that,  when  served,  the  pieces  do  not  lose  their 
shape  readily.  Gum  tragacanth  furnishes  a  desirable 
substitute  for  gelatin.  Corn  starch  and  flour  are  other 
substances  frequently  used  as  binders. 

Ice  cream  made  by  freezing  a  mixture  of  pure,  rich 
cream,  sugar,  and  flavoring  material  contains  too  much  fat 
to  be  easily  digested  by  many  people  when  the  usual 
quantity  is  eaten,  and  so  is  objected  to  on  account  of  its 
"  richness."  On  the  other  hand,  ice  cream  low  in  milk 
fat  has  a  coarse,  granular  structure,  due  to  the  crystals  of 
ice  that  separate  from  the  mixture.  Ice  cream  contain- 
ing from  14  %  to  18  %  of  fat  is  considered  to  be  best  for 
general  use. 

The  use  of  coal  tar  dyes  as  coloring  matter  for  ice  cream 
is  both  unnecessary  and  unwise.  Ice  cream  is  most  exten- 
sively used  during  the  summer  months  when  plenty  of 
fresh  fruits  may  be  obtained  for  flavoring  materials.  These 
give  the  finished  product  unexcelled  flavors  and  pleasing 
colors.  It  is  better  to  add  the  fruit  at  the  time  the  ice 


BUTTER  295 

cream  commences  to  thicken  in  the  freezer,  otherwise  the 
fruit  acids  may  cause  the  cream  to  curdle,  and  the  fruit  is 
likely  to  be  frozen  too  hard. 

All  that  has  been  said  in  the  preceding  chapter  concern- 
ing the  dangers  arising  from  the  use  of  impure  milk, 
applies  with  greater  force  to  impure  ice  cream.  Dr.  Wiley 
states  that  263  samples  of  ice  cream,  which  were  collected 
and  examined,  in  one  of  our  large  cities,  contained  on  the 
average  over  26,000,000  organisms  per  cubic  centimeter, 
and  that  16  of  the  samples  contained  100,000,000  per  cubic 
centimeter.  Of  the  115  samples  examined  for  disease- 
producing  bacteria,  38.3%  were  found  to  be  infected. 
The  popularity  of  ice  cream  as  an  article  of  food  during 
the  summer  months,  together  with  the  fact  that  a  consid- 
erable portion  of  the  ice  cream  sold  is  eaten  by  children, 
should  cause  the  people  to  demand  the  enactment  and 
enforcement  of  stringent  laws  governing  its  manufacture, 
storage,  and  sale.  At  present,  the  consumer  seldom  knows 
what  the  ice  cream  he  purchases  contains,  under  what  con- 
ditions it  was  made,  where  it  has  been  stored,  or  the  clean- 
liness of  the  persons  who  have  handled  it. 

273.  Butter.  —  When  cream  is  beaten  or  agitated  for 
some  time,  the  fat  globules  are  broken  down  and  the  fat 
crystals  collect  in  lumps  of  butter.  The  butter  is  washed 
with  water,  and  "  worked  "  to  squeeze  out  the  buttermilk 
which  has  remained  entangled  between  the  particles  of  fat. 
The  product  thus  prepared  may  be  sold  directly  as  unsalted 
or  sweet  butter,  or  it  may  be  thoroughly  mixed  with  salt 
and  sold  as  butter.  Unsalted  butter  has  poor  keeping 
qualities,  while  good  salted  butter  keeps  well  in  a  clean, 
cool  place.  Good  cream,  great  care  in  preparation,  non- 
porous  containers,  a  cool  place  free  from  odors,  and  cleanli- 
ness from  beginning  to  end  are  essential  to  the  keeping 


296      CREAM,   ICE   CREAM,  BUTTER,  AND   CHEESE 

qualities  of  butter.     Poor  butter  is  one  of  the  most  com- 
mon articles  of  commerce. 

274.  Process  or  Renovated  Butter.  —  The  fact  that  much 
of  the  butter  placed  on  the  market  soon  becomes  rancid 
has  led  to  the  development  of  methods  for  the  conversion 
of  "  strong "  butter  into  a  substance  closely  resembling 
fresh  butter.     One  process  employed  for  this  purpose  is 
essentially  as  follows : 

The  rancid  butter  is  taken  to  the  factory,  where  it  is 
dumped  into  a  melting  vat.  The  clear,  molten  fat  is 
strained  and  then  raised  to  a  temperature  of  120°  C. 
After  the  curd  has  settled  and  has  been  separated,  streams 
of  air  are  passed  through  the  warm  oil  for  several  hours. 
The  air  removes  disagreeable  odors  and  produces  a  clear, 
nearly  tasteless  oil,  which,  after  being  churned  with  a 
mixture  of  sweet  and  sour  buttermilk,  is  gathered  and 
salt  is  worked  into  it. 

275.  Adulterated  Butter. — This  term  has  been  applied  to 
all  mixtures  of  butter  with  cheaper  fats  and  to  all  substi- 
tutes for  butter.     The  adulteration  of  butter  with  the  pur- 
pose of  deceiving  the  consumer  has  been  prohibited  by  law. 
At  present,  very  few  persons  are  deceived  by  the  purchase 
of  spurious  butter.     The  term  adulterated  butter  should 
not   be    applied    to    oleomargarine,    butterine,    renovated 
butter,  and  similar  preparations  sold  under  their  true  names. 

276.  Oleomargarine  and  Butterine.  —  These  and   similar 
preparations  are  sold  extensively  as  substitutes  for  butter. 
Oleomargarine   is  said   to   have  originated   through  the 
efforts  of  a  French  chemist,  Mege-Mouries,  to  furnish  the 
poorer  classes  and  sailors  of  France  with  a  cheap  and  other- 
wise desirable  substitute  for  butter.      He  tried  to  make 
butter  by  an  artificial  process.     His  first  description  of  a 


CHEESE  297 

method  for  making  imitation  butter  on  a  large  scale 
appeared  in  1870.  A  patent  for  the  manufacture  of  an 
artificial  butter  was  granted  by  the  United  States  in  1873, 
and  since  that  time  many  other  patents  have  been  issued 
for  the  manufacture  of  substitutes  for  butter. 

In  general,  oleomargarine  consists  of  various  mixtures 
of  fats.  These  are  beef  fats  of  various  kinds,  neutral  lard, 
cottonseed  oil,  and  palm  oil.  The  mixtures  are  agitated 
with  milk,  which  has  generally  been  soured  with  pure 
cultures  of  lactic  acid  bacteria,  and  then  colored  and 
salted,  so  that  the  product  very  closely  resembles  butter. 
Butterine  differs  from  oleomargarine  in  that  it  contains  a 
certain  percentage  of  butter. 

Great  care  and  cleanliness  are  exercised  in  the  prepara- 
tion of  artificial  butters  and  they  are  generally  considered 
wholesome,  though  not  so  desirable  as  pure  butter  for  fry- 
ing, or  for  table  use,  on  account  of  the  unpleasant  odor 
on  hot  food. 

277.  Cheese  is  made  by  curdling  milk  by  means  of  a 
dilute  acid,  or  by  the   ferment  contained  in   rennet,  and 
then  bringing  about  desirable  flavors  by  the  addition  of 
salt  and,  especially,   by  permitting  various  organisms  to 
act  upon  the  curd.     An  herb,  for  example,  sage,  is  some- 
times used  for  additional  flavoring  material. 

278.  Cottage  Cheese,   schmierkase,    Dutch   cheese,   sour 
milk  cheese,  and   Philadelphia  cream  cheese  are  various 
names  applied  to  a  cheese  produced  by  the  action  of  lactic 
acid  bacteria  on  milk.     In  the  home,  the  usual  method 
employed  for  making  cottage  cheese  is  to  let  the  milk  sour 
until  a  thick  curd  has  formed.     The  curdled  milk  is  heated 
to  about  100°  F.  and  stirred  until  the  whey  appears  clear. 
Then  the  product  is  placed  in  a  cheesecloth  bag  which  is 
hung  so  that  the  whey  will  drain  off.     The  moist  curd 


298      CREAM,   ICE   CREAM,   BUTTER,   AND    CHEESE 

is  then  mixed  with  sufficient  salt  and  cream  to  give  the 
product  the  desired  flavor  and  richness. 

When  cream  cheese  is  manufactured  on  a  large  scale,  a 
rapid  souring  of  sweet  skim  milk  is  brought  about  by  the 
use  of  pure  cultures  of  lactic  acid  bacteria.  The  curd 
produced  is  separated  and  then  treated  in  a  manner  similar 
to  the  homemade  article.  Cream  cheese  does  not  keep 
well. 

279.  American  Cheese.  —  A  ferment  that  is  extremely 
active  in  curdling  milk  is  produced  in  the  fourth  stomach 
of  the  calf.  Rennet  is  the  commercial  name  for  a  prepa- 
ration of  this  ferment.  The  active  principle  (enzyme)  of 
rennet  is  so  powerful  that  1  part  of  rennet  will  bring 
about  the  desired  change  in  400,000  times  its  weight  of 
casein.  Rennet  is  commonly  used  in  making  cheese  from 
sweet  milk.  The  process  may  be  briefly  outlined  as 
follows :  sweet  skimmed  milk  is  heated  to  about  86°  F. 
and  the  rennet  added.  After  the  curd  has  formed,  the 
whey  is  allowed  to  sour,  in  order  to  bring  about  a  more 
complete  separation  of  the  curd.  The  curd  is  collected, 
freed  from  whey,  salted,  and  pressed.  The  fresh  ("green  ") 
cheese  is  then  allowed  to  ripen,  that  is,  it  is  allowed  to 
stand  until  processes  of  fermentation  have  brought  about 
the  desired  flavor  (Fig.  89).  Several  months  were  for- 
merly required  for  a  cheese  to  ripen  satisfactorily. 
Artificial  processes  for  producing  a  flavor  similar  to  that 
of  a  well-ripened  cheese  have  been  introduced  in  cheese 
factories,  so  that  the  time  required  for  the  conversion  of 
the  "green"  cheese  into  a  palatable  product  has  been 
greatly  lessened.  The  richness  of  the  cheese  varies 
greatly  with  the  amount  of  cream  contained  in  the  milk 
from  which  it  was  made,  and  with  the  amount  of  fat 
rubbed  over  the  cheese  during  the  process  of  ripening. 


RIPENING  OF  CHEESE 


299 


Copyright  by  Underwood  &  Underwood,  N.  Y. 

FIG.  89.  — RIPENING  OF  CHEESE. 


BOO     CREAM,   ICE   CREAM,  BUTTER,   AND   CHEESE 

Other  varieties  of  cheese  are  too  numerous  to  be  men- 
tioned in  an  elementary  book.  They  are  made  from  the 
milk  of  either  the  cow  or  the  goat.  Their  flavor  and  con- 
sistency differ  greatly  with  the  kind  of  organisms  that 
take  part  in  the  process  of  ripening. 

Cheese  is  a  highly  nitrogenous  substance,  the  food 
value  of  which  is  not  generally  appreciated. 

SUMMARY 

Cream  consists  of  the  fat  globules  which  rise  slowly  and  form 
a  layer  on  top  of  milk. 

Separation  of  the  Cream  from  the  remainder  of  the  milk  is 
brought  about  rapidly  by  the  use  of  a  centrifugal  machine,  called 
a  separator. 

Whipped  Cream  is  the  foam  produced  by  beating  cream  until 
the  fat  globules  are  broken  and  mixed  with  air. 

Ice  Cream  is  generally  supposed  to  be  a  frozen  mixture  of  cream, 
sugar,  and  flavoring  material.  Almost  any  frozen  custard,  or 
milk  thickened  by  the  use  of  gelatine,  or  gum  tragacanth,  sweet- 
ened, flavored,  and  frozen,  passes  for  ice  cream. 

The  Manufacture  and  Handling  of  Ice  Cream  should  be  conducted 
with  a  high  degree  of  cleanliness,  as  ice  cream  furnishes  a  rich 
culture  medium  for  disease-producing  bacteria. 

Sweet  Butter  is  made  by  agitating  cream  until  the  fat  globules 
are  broken  and  the  crystallized  fat  has  collected  in  lumps.  The 
fat  is  then  washed  and  worked,  to  squeeze  out  the  buttermilk  that 
has  remained  between  the  particles. 

Butter  is  sweet  butter  that  has  been  mixed  with  salt. 

Process  or  Renovated  Butter  is  made  by  converting  rancid  butter 
into  a  product  closely  resembling  fresh  butter. 

Oleomargarine  is  a  general  name  applied  to  artificial  butters. 

Butterine  differs  from  oleomargarine  in  that  it  contains  some 
butter. 


EXERCISES  301 

Cheese  is  the  protein  of  milk  obtained  by  curdling  milk  with  an 
acid  or  more  generally  by  the  ferment  of  rennet.  Desirable  fla- 
vors are  produced  by  salt,  bacteria,  and  other  organisms. 

EXERCISES 

1.  What  is  cream  ? 

2.  Why  are  separators  used  in  modern  dairies-? 

3.  What  is  the  lowest  percentage  of   fat  that  should  be 
present  in  cream  ? 

4.  What   is   whipped    cream  ?      How   should    cream    be 
treated  preparatory  to  being  whipped? 

5.  What  is"Viscogen"? 

6.  What  is  ice  cream  ? 

7.  Why  should  great  cleanliness  be  exercised  in  the  manu- 
facture and  handling  of  ice  cream  ? 

8.  Why  should  the  use  of  dyes  in  the  making  of  ice  cream 
be  discouraged  ? 

9.  Why  should  stringent  laws  regulating  the  manufacture, 
handling,  and  sale  of  ice  cream  be  enacted  and  enforced  ? 

10.  What  advantage  would  there  be  in  requiring  that  the 
formula  used  in  making  the  ice  cream  be  furnished  to  the  pur- 
chaser on  request  ? 

11.  How  is  butter  made? 

12.  How  does  sweet  butter  differ  from  butter? 

13.  What  is  process  or  renovated  butter  ? 

14.  What  is  oleomargarine  ? 

15.  How  does  butterine  differ  from  oleomargarine  ? 

16.  Why  should  not  oleomargarine  be   called  adulterated 
butter  ? 

17.  What  advantages  are  there  in  the  use  of  oleomargarine, 
or  butterine,  instead  of  butter  ?     What  disadvantage  ? 

18.  What  is  cheese  ? 

19.  How  is  cottage  cheese  made  ? 

20.  Briefly  describe  the  manufacture  of  American  cheese. 


CHAPTER   XXVI 

CLEANING  AND  LAUNDERING 

280.  The  Nature  of  the  Cleaning  Process.  —  The  operations 
of  cleaning  frequently  involve  both  physical  and  chemical 
processes.     Dirt,  which  is,  after  all,  only  matter  in  the 
wrong  place,  can  sometimes  be  removed  by  the  mechanical 
means  of  brushing,  shaking,  or  agitation  with  water,  the 
object  being  to  first  loosen  the  dirt  by  friction  and  then 
carry   it   away  by  currents   of   air  or  water   (Fig.   90). 
Usually,  however,  there  is  enough  greasy  matter  present 
to  cause  the  dirt  to  adhere  so  that  these  means  alone  are 
not  effective.     In  such  cases  a  substance  must  be  used 
that  will  dissolve  grease.     Soap  is  employed  ordinarily 
to  accomplish  this  end. 

281.  Soap.  —  All  the  strong  bases,  such  as  sodium  and 
potassium  hydroxides,  have  the  power  of  acting  chemically 
on  fats  and  greases.     They  cannot  often  be  used  directly 
as  cleaning  agents,  however,  because  they  are  extremely 
caustic  and  act  readily  on  all  sorts  of  organic  matter. 
For  cleaning  floors,  greasy  ironware,  or  sinks,  solutions 
of  bases  may  be  used,  if  the  person  who  handles  them  is 
careful  not  to  get  them  on  his  flesh  or  clothing.     But  for 
ordinary   cleaning   operations   we    must   use   the   highly 
modified  bases  which  we  call  soaps.     These  also  have  the 
power  of  dissolving  fats  or  grease,  but,  if  pure,  they  are 
not  caustic  in  their  action  on  the  skin  and  fabrics. 

282.  The  Manufacture  of  Soap.  —  The  essential  step  in  the 
manufacture  of  soap  is  a  chemical  action  between  a  strong 

302 


PRIMITIVE    WASHING 


303 


304  CLEANING  AND  LAUNDERING 

base  and  a  fat.  Fats  are  organic  salts,  analogous  to  in- 
organic salts  like  sodium  sulphate,  Na2SO4.  For  example, 
beef  fat  is  mainly  glyceryl  stearate,  C3H5(C18H35O2)3 ;  the 
part  of  a  metal  is  played  by  the  glyceryl  radical,  C3H5; 
the  acid  radical,  C18H35O2,  is  that  of  stearic  acid, 
HC18H35O2.  Other  fats  are  mixtures  of  glyceryl  salts. 
The  main  acid  constituent  may  be  from  oleic,  palmitic,  or 
some  other  acid.  When  any  of  these  fats  is  boiled  with 
sodium  hydroxide,  a  soap  and  glycerin  result  from  the 
action : 

CoHKCCioiIoeOn^o  -{-  3  NaOH  — >- 


J 


glyceryl  sodium 

stearate  hydroxide 
(fat) 

3NaC18H3502  +C3H5(OH)3 

sodium  glyceryl 

stearate  hydroxide 

(soap)  (glycerin) 


In  the  actual  manufacturing  operation,  the  boiling  of 
soap  is  often  carried  out  in  huge  kettles  that  will  yield  20  to 
30  tons  of  the  product.  The  operation  lasts  from  several 
hours  to  two  or  three  days.  At  the  end  of  this  period, 
common  salt  is  added.  Soap  is  insoluble  in  brine,  and 
hence  separates  and  rises  to  the  top  of  the  kettle.  The 
salty  liquid  at  the  bottom  is  drawn  oft',  and  in  most  cases 
is  distilled  under  diminished  pressure  to  obtain  the  glyce- 
rin which  it  contains.  The  "  salting  out,"  as  it  is  termed, 
also  affords  a  means  of  getting  rid  of  the  excess  of  base 
that  would  otherwise  remain  in  the  soap. 

Laundry  soaps  are  made  from  animal  fat,  refuse  fat 
from  the  kitchen,  palm  oil,  and  cottonseed  oil.  Cocoa- 
nut  oil  can  be  made  into  a  soap  by  a  "cold"  process, 
provided  that  a  carefully  calculated  quantity  of  base  is 
used.  In  this  soap  the  glycerin  remains  in  the.  finished 
article. 


ADULTERATIONS  IN  SOAP  305 

If  potassium  hydroxide  is  used  as  the  base,  a  soft  soap 
results.  "  Green  soap  "  and  shaving  soap  are  potassium 
soaps,  at  least  in  part.  Floating  soaps  are  obtained  by 
beating  air  into  the  product  before  allowing  it  to  harden. 
Castile  soap  is  made  from  an  inferior  grade  of  olive  oil. 

283.  'Quality  of  Soap.  —  This  depends   chiefly  on   two 
factors.     One  of  these  is  the  use  of  a  fat  that  is  fairly 
pure  and  that  will  not  become  rancid  in  the  soap ;  the 
other  is  the  avoidance  of  an  excess   of   base,   which,   if 
present,  makes  the  soap  caustic  and  injurious  to  the  skin 
and  fabrics. 

284.  Adulterations  in  Soaps.  — Soaps  are  very  much  sub- 
ject to  adulteration.     Sodium  silicate,  a  cheap  sul   Lance 
which  has  a  certain  amount  of  cleansing  power,  i,s  fre- 
quently used  for  this  purpose.     Its  use  is  undesirable ; 
it  is  injurious  to  fabrics  and  it  tends  to  make  the  soap 
retain  a  high  proportion  of  water.     This  makes  the  soap 
deceptive  in  bulk  and  makes  it  waste  very  rapidly  in  use. 
Rosin  is  nearly  always  added  to  laundry  soaps  and  is  the 
reason  for  their  yellow  color  and  strong  lathering  prop- 
erties.    Used  in  proper  quantity  rosin  is  not  an  adulter- 
ant, because  it  combines  with  the  base  and  makes  a  rosin 
soap,  and  the  formation  of  lather  plays  an  important  part 
in  the  cleaning  operation.      Water  is  considered  an  adul- 
terant in  soaps  when  present  in  quantities  above  25%. 
It  makes  the  soap  soft,  so  that  it  wastes  rapidly.     Many 
other  substances  are  used  in  adulterating  soaps.     Almost 
anything  that  is  cheap  and  bulky  is  used  for  the  purpose. 
Toilet  soaps  are  frequently  adulterated  with  substances  of 
supposed  medicinal  value. 


285.    Special  Soaps. — The  only  requirements  for  good 
toilet  soaps  are  that  they  be  made  from  purified  fats,  and 


306  CLEANING  AND  LAUNDERING 

that  they  do  not  contain  an  excess  of  base.  This  latter- 
requirement  is  particularly  necessary,  since  the  caustic 
base  would  roughen  the  skin.  Castile  soap,  when  good, 
makes  a  thoroughly  satisfactory  toilet  soap. 

Powdered  Soaps.  For  toilet  purposes  these  are  made 
by  simply  grinding  a  thoroughly  dried  toilet  soap  of  good 
quality.  For  laundry  purposes,  the  trimmings  of  cake 
soap  are  used,  and  soda  ash  (sodium  carbonate)  is  nearly 
always  added. 

Shaving  Soaps.  The  strong  lathering  properties  of 
these  soaps  are  secured  by  addition  of  rosin  and  they  are 
always  potassium  soaps  in  part.  Sometimes  they  are 
made  from  cocoanut  oil  with  the  addition  of  stearic  acid. 

Liquid  soaps  are  less  used  than  powdered  soaps. 

Scouring  soaps  are  made  from  laundry  soaps  by  addition 
of  ground  quartz,  pumice,  or  other  abrasive.  They  are 
dried  in  molds. 


286-  Other  Cleaning  Agents.  —  Washing  soda, 
sodium  carbonate,  resembles  strong  bases  like  sodium  and 
potassium  hydroxides  in  its  chemical  properties,  but  is 
much  more  moderate  in  its  action.  A  strong  solution, 
however,  is  injurious  to  the  hands  and  fabrics.  But  its 
power  to  dissolve  grease  makes  it  a  great  aid  in  cleaning 
coarse  or  very  dirty  articles,  and  its  use  for  this  purpose 
is  not  objectionable,  especially  if  the  washing  is  done  in  a 
machine. 

Borax,  Na2B4O7,  a  substance  that  is  found  ready 
made  in  nature,  represents  a  still  more  moderate  form  of 
alkali,  but  one  that  also  has  the  power  of  dissolving  grease. 
It  is  a  very  valuable  cleaning  agent,  and  it  will  cleanse 
even  a  very  dirty  cloth  to  clear  whiteness.  Its  use  is 
somewhat  limited  owing  to  its  comparative  high  cost. 

Ammonia  water,  ammonium  hydroxide,  NH4OH,  which 


WASHING 


307 


is  practically  a  solution  of  ammonia,  NH3  in  water,  also 
acts  like  sodium  hydroxide,  but  with  moderated  intensity. 
It  is  particularly  valuable  because  it  is  volatile.  Its 
solution  breaks  up  into  its  constituents  according  to  the 
equation : 

NH4OH  — »-  NH3  +  H2O 

ammonium  ammonia      water  • 

hydroxide 

A  strong  solution  may  be  applied  directly  to  the-  clothing 
because  it  evaporates  in  a  few  minutes  and  does  not 
remain  in  contact  with  the  goods  long  enough  to  affect  it 
harmfully.  It  is  useful  for  removing  grease  spots  from 
the  clothing. 

287.  Washing.  —  The  first  step  in  the  laundering  of 
clothes  is  the  combined  action  of  vigorous  mechanical 
agitation  and  the  solvent  power  of  soap  solution.  In 
laundries,  and  increasingly  in  homes,  work  formerly  done 


Copyright  by  Underwood  &  Underwood,  N.  Y. 

FIG.  91. — AN  ELECTRIC  LAUNDRY. 


308  CLEANING  AND  LAUNDERING 

by  hand  is  now  done  by  washing  machines  (Fig.  91). 
These  machines  save  a  great  deal  of  labor  and  give  very 
satisfactory  results.  White  materials  of  strong  texture 
will  stand  vigorous  treatment ;  a  small  amount  of  wash- 
ing soda  and  a  high  temperature  are  quite  helpful. 
Colored  fabrics  must  be  handled  more  carefully.  Kero- 
sene oil,  which  is  an  excellent  grease  solvent,  is  added  to 
the  hot  soap  solution  with  good  results.  Thorough  rins- 
ing is  needed  to  remove  all  soap  from  the  garments. 

288.  Bluing.  —  The  next  step  in  the  laundering  of  white 
goods    is   bluing.     The  soap  and  heat  used   in    washing 
ht*&e  a  tendency  to  develop  a  yellow  tint.     Blue  is  the 
complementary   color    to    yellow,    and     a    treatment    of 
the  goods  in  a  bath  of  a  blue  color  neutralizes  the  yellow 
tint.     Various  blue  dyes,  and  the  pigments,  Prussian  blue 
and  ultramarine,  are  used  for  the  purpose.     The  pigments 
are  preferred  because  they  have  less  tendency  to  accumu- 
late in  the  cloth  with  successive  washings.     Ultramarine 
is  better  than  Prussian  blue,  owing  to  the  fact  that  the 
latter  is  an  iron  compound  which  reacts  with  bases  or 
alkalies  to  form  ferric  hydroxide  : 

Fe4[Fe(CN)6]3  +  12  NaOH  — >- 

Prussian  blue  sodium  hydroxide 

4  Fe(OH)3  +  3Na4Fe(CN)6 

ferric  hydroxide        sodium  ferrocyanide 

Hence  red  spots  of  what  is  practically  iron  rust  sometimes 
develop  on  clothing  that  has  been  blued  with  Prussian 
blue.  If  this  happens,  it  is  because  all  of  the  soap  was 
not  rinsed  from  the  clothes  before  they  were  put  in  the 
bluing  water. 

289.  Starching.  —  Starch  is  used  to  make  garments  stiff, 
and  also  to  keep  them  clean  longer.     It  is  applied  both 


DRY  CLEANING  309 

cooked  and  uncooked.  Starch  is  found  in  many  plants. 
The  microscope  shows  that  it  is  composed  of  granules  or 
cells.  When  starch  is  boiled  with  water,  these  cells  burst 
open  and  the  cooked  mass  acquires  a  gelatinous  character. 
This  characteristic  makes  it  adhere  firmly  to  the  goods 
after  it  has  been  worked  into  the  fibers.  For  starching 
collars,  uncooked  starch  is  used,  probably  for  -the  reason 
that  the  goods  will  take  more  starch  cells  in  this  condition. 
During  the  ironing,  the  starch  becomes  at  least  partly 
cooked  and  thus  acquires  the  desirable  gelatinous  quality 
and  gloss. 

290.  Dry  Cleaning. — Gasoline  and  benzene  are  orf  ac 
liquids  much  used  for  cleaning  purposes  because  .ney 
are  powerful  solvents  for  grease  and  are  also  readily 
volatile.  With  their  aid  we  can  cleanse  fabrics  that  will" 
not  stand  the  use  of  soap  and  water.  Silk  and  woolen 
goods  are  best  cleaned  in  this  manner.  The  solvent  im- 
mediately dissolves  any  oily  matter  that  is  present  and 
the  dirt  is  carried  away  by  the  currents  of  liquid  that 
flow  through  the  fibers. 

GREAT  DANGER  attends  the  use  of  gasoline  in 
cleaning.  This  is  due  to  the  fact  that  this  inflammable 
liquid  is  so  volatile  that  if  it  is  used  in  any  closed  space, 
such  as  a  room,  the  air  very  quickly  contains  a  consider- 
able quantity  of  the  solvent  in  the  form  of  a  gas.  The 
mixture  of  oxygen  and  hydrocarbon  vapor  is  highly  explo- 
sive. A  light  or  spark,  no  matter  how  small,  is  enough  to 
set  it  off.  Serious  accidents  have  happened  from  the  com- 
mon, but  erroneous,  belief  that  it  is  the  liquid  gaso- 
line which  is  explosive.  It  is  not  the  liquid,  but  the 
mixture  of  air  with  gasoline  vapor,  that  is  dangerous. 

All  cleaning  with  gasoline  or  other  volatile,  inflammable 
liquid  should  be  carried  on  out  of  doors,  or  in  a  room 


BIO  CLEANING  AND  LAUNDERING 

through  which  a  strong  draft  of  air  is  blowing.  Any 
possibility  of  enough  of  the  gas  collecting  to  form  an  ex- 
plosive mixture,  is  thus  avoided. 

291.  Spots  and  Stains.  —  Where    ordinary    washing    or 
solvent  action  does  not    suffice,   special    chemical   treat- 
ment is  necessary  to  remove  spots  and  stains.     Methods 
for  the  removal  of  various  kinds  of  stains  may  be  classified 
under  certain  general  principles. 

Neutralization  is  used  when  the  spot  is  due  to  either 
an  acid  or  a  base.  For  acids,  ammonium  hydroxide*  is 
applied.  Bases  should  be  treated  with  a  weak  solution 
of  acetic  acid  (vinegar),  and  the  excess  of  the  acid  neu- 
tralized with  ammonium  hydroxide.  Bleaching  is  em- 
ployed where  the  spot  has  been  formed  from  the  action  of 
a  dye  or  of  fruit  juice.  Javelle  water,  an  alkaline  solution 
that  readily  liberates  chlorine,  is  useful  for  this  purpose, 
or  sulphur  dioxide  may  be  used  where  chlorine  would  be 
too  active,  as  in  the  case  of  silk  or  wool. 

Ink  stains  are  often  removed  by  a  reducing  agent. 
Most  inks  contain  ferrous  tannate  which  on  exposure  to 
air  becomes  ferric  tannate.  The  latter  is  a  substance 
which  gives  to  ink  its  final  black  color.  By  the  action  of 
a  reducing  agent,  such  as  oxalic  acid,  the  ferric  tannate  is 
again  changed  to  a  ferrous  compound  which  is  soluble 
and  can  be  washed  away.  The  primary  dye  that  is  in 
the  ink  may  remain  and  require  removal  by  bleaching  with 
a  solution  of  bleaching  powder  acidified  with  oxalic  acid. 
In  removing  spots  it  is  well  to  first  test  a  small  piece  of 
the  goods  with  the  agent  that  it  is  proposed  to  use,  in 
order  to  make  sure  that  neither  the  dye  nor  the  fabric 
will  be  injured. 

292.  The  Use  of   Bleaching  Agents  in  Laundering.  —  In 

commercial  laundries  it  is  not  uncommon  to  make  use  of 


SUMMARY  311 

bleaching  solutions  to  hasten  the  operation  of  cleaning. 
This  is  not  desirable,  since  repeated  use  of  such  solutions 
tends  to  disintegrate  the  cloth.  Chlorine  is  frequently 
used  to  accomplish  the  bleaching.  It  can  be  obtained 
from  chloride  of  lime,  CaO2Cl2,  by  the  addition  of  dilute 
acid.  A  process  for  obtaining  chlorine  by  the  electrolysis 
of  sea  water  (brine)  is  rapidly  coming  into  use.  Javelle 
water  is  also  used  as  a  source  of  chlorine.  It  is  prepared 
by  treating  chloride  of  lime  with  sodium  carbonate, 
Na2CO3  (washing  soda),  or  potassium  carbonate,  in  water 
solution. 

SUMMARY 

In  Cleaning  it  is  first  necessary  to  remove  oily  or  greasy  matter 
that  causes  the  dirt  to  adhere  to  the  soiled  article.  Soaps  are 
used  because  they  are  good  solvents  for  grease  and  are  them- 
selves soluble  in  water. 

Soaps  are  made  by  boiling  solutions  of  strong  bases,  usually 
sodium  hydroxide,  with  fats  or  oils.  The  soap,  which  is  the  so- 
dium or  potassium  salt  of  a  fatty  acid  (stearic,  palmitic,  oleic),  and 
glycerin  result  from  the  action. 

Toilet  Soap  should  not  contain  any  free  base,  nor  more  than 
25  %  of  water. 

Laundry  Soaps  are  made  with  the  addition  of  rosin  during  the 
operation  of  boiling.  This  gives  them  strong  lathering  properties. 

Special  Soaps  and  Cleaning  Powders  generally  contain  sodium 
carbonate,  which  makes  them  rather  caustic  in  action.  Borax, 
which  is  not  so  caustic  as  the  sodium  carbonate,  is  also  used. 

Scouring  Soaps  are  made  from  ordinary  soap  by  the  addition  of 
a  powdered  abrasive  such  as  pumice  or  quartz. 

Washing  Soda,  Ammonia  Water,  or  Borax  can  be  used  where  a 
stronger  grease  solvent  is  desired  than  that  which  can  be  obtained 
by  the  use  of  soaps. 


312  CLEANING  AND  LAUNDERING 

The  Operation  of  Washing  is  dependent  on  the  solvent  action  of 
the  soap  solution  plus  the  mechanical  action  of  moving  currents  of 
water. 

Bluing  is  used  to  neutralize  the  yellow  tint  which  washing  de- 
velops in  white  goods.  Dyes,  Prussian  blue,  or  ultramarine  are 
used.  The  last-named  substance  is  the  best. 

Starching  stiffens  clothes  and  makes  them  keep  clean  longer. 

Dry  Cleaning  is  accomplished  with  organic  solvents  that  evap- 
orate quickly  from  the  cloth.  They  act  in  the  same  way  as  water 
except  that  they  themselves  are  good  grease  solvents. 

Gasoline  and  benzene  are  the  substances  most  used  for  dry 
cleaning. 

The  use  of  these  inflammable  liquids  for  cleaning  purposes  is  very 
dangerous.  A  mixture  of  their  vapors  with  air  is  highly  explo- 
sive and  can  be  set  off  by  a  minute  spark  or  flame  at  some 
distance  from  the  place  where  the  cleaning  is  being  done.  Such 
work  should  be  done  out  of  doors. 

Spots  and  Stains  require  special  chemical  treatment  according 
to  the  nature  of  the  spot. 

EXERCISES 

1.  How   does   water   act   mechanically  in   cleaning   opera- 
tions ?     What  part  does  soap  play  ? 

2.  Would  gasoline  and  water  make  as  satisfactory  a  com- 
bination for  cleaning  the  hands  as  soap .  and  water  ?     Explain. 

3.  Explain  the   process   of   making   soap.     Why   is    there 
frequently   free   base   in   finished   soap  ?     How   can   this   be 
avoided  ? 

4.  Is   there   any   objection    to   free    base   in  toilet   soap? 
Why  ?     In  laundry  soap  ?     Explain. 

5.  Is    a   lathering    property   desirable    in    soaps?     Why? 
How  is  it  obtained  ? 

6.  Why  is   it  not  desirable   to  have   more  than  25  %  of 
water  in  soaps? 


EXERCISES  313 

7.  Name  some  adulterants  commonly  used  in  soaps.     Why 
is  their  use  objectionable  ? 

8.  "  Medicated "  soaps  are  usually  sold  at  a  higher  price 
than  ordinary  good  toilet  soaps;  is  this  extra  price  justifiable? 

9.  What  is  the  chief  difference  between  sodium  soaps  and 
potassium  soaps?      For  what  purposes    are   potassium  soaps 
desirable  ?  « 

10.  What   is   a   scouring   soap?     From  the  standpoint  of 
economy,  what  could  you  substitute  for  these  with  advantage 
for  rough  cleaning  ? 

11.  Why  is   ammonia  water   useful   in  cleaning?      What 
advantage  has  it  over  soap  ?     Over  washing  soda  ? 

12.  Which  is   preferable   for   cleaning   purposes,  washing 
soda  or  borax  ?     Discuss. 

13.  What   advantage   is   there   in   the   use   of   a   washing 
machine  for  laundry  work!* 

14.  If  iron  rust  spots  appear  on   clothing   after  washing, 
what  operation  in  the  washing  process  may  have  caused  them  ? 
How  would  you  avoid  trouble  of  this  sort  ? 

15.  Why  does  a  change   take  place  in  the  appearance  of 
a  mixture  of  starch  and  water  as  it  is  being  cooked  ?     How  is 
starch  applied  for  making  collars,  etc.,  very  stiff? 

16.  What  kinds  of  goods  are  best  cleaned  by  dry  cleaning  ? 
Why? 

17.  Explain  the  process  of  dry  cleaning. 

18.  State  precautions  to  be  observed  in  the  use  of   gasoline 
for  cleaning  purposes.     Give  reasons. 

19.  How  would  you  remove  a  grease  spot  from  a  woolen 
suit  ?     An  acid  spot  ? 

20.  What  is  Javelle  water  ?     How  is  it  made  ?     Why  is  it 
useful  in  the  household  ?     Why  should  this  solution  not  be 
allowed   to   remain  long  in  contact  with  cloth  ?     How  would 
you  counteract  its  undesirable  effects  ? 


CHAPTER   XXVII 

INK 

293.  Writing  Inks  may    be  roughly  divided  into  three 
classes :  those  whose  color  depends  on  iron  salts  of  one  or 
more  of  the  tannic  acids,  or  tannins;  those  whose  color  is 
due  to  an  aniline  dye;  and  those  whose  color  is  due  to 
finely  divided  carbon. 

Tannin  and  tannic  acid  are  terms  applied  to  a  class  of 
substances  that  are  soluble  in  water,  possess  a  bitter, 
astringent  taste,  and  have  the  property  of  converting  the 
skins  of  animals  into  leather.  They  react  with  ferric  salts 
to  produce  a  nearly  black  precipitate.  Many  plants  yield 
tannins,  and  the  tannin  is  generally  named  from  the  plant 
producing  it.  Thus  we  have  chestnut  tannin,  oak  bark 
tannin,  and  sumac  tannin. 

294.  Galls  are  morbid  growths  produced  on  many  plants 
when  their  twigs  are  punctured  by  insects.     These  par- 
take more  or  less  of  the  nature  of  the  plant  on  which  they 
grow.     One  variety  of  such  growths  has  for  many  years 
been  of  importance  in  the  manufacture  of  ink.     An  insect, 
commonly   called  the  gall-insect  or  gall-fly,   pierces   the 
tissue  of  the  branch  of  an  oak  tree,  and  deposits  an  egg 
together  with  a  small  quantity  of  a  poisonous  fluid  in  the 
cavity.     The  fluid  causes  a  growth,  known  as  a  gall,  to 
develop  rapidly,  and  in  this  the  egg  hatches  and  the  insect 
matures.     The  mature  insect  finally  eats  its  way  out  of  the 
gall  and  flys  away.     Oak-galls,  or  nutgalls  as  they  are 
called,  are  articles  of  commerce.     They  are  globular  in 

314 


IRON  INKS 


315 


"a  .** 


shape  and  are  generally  about  half  an  inch  in  diameter 
(Fig.  92).  Galls  that  have  not  been  punctured  are  con- 
sidered by  ink  manu- 
facturers to  be  of  su- 
perior quality.  Good 
nutgalls  are  quite  com-, 
pact  and  heavy.  The 
tannic  acid  derived  from 
nutgalls  is  known  as 
gallotannic  acid.  A  good 
quality  of  nutgalls 
yields  about  25  %  of 
tannic  acid.  The  acid 
can  be  obtained  from 
finely  pulverized  galls 
by  soaking  the  powder 
in  ether  and  then  filter- 
ing, in  order  to  separate 
the  solution  of  the  acid 

from  the  insoluble  mass,  and  then  evaporating  the  solu- 
tion to  dryness.  When  boiled  with  water,  the  tannic  acid 
combines  with  the  water  and  forms  gallic  acid;  that  is, 
tannic  acid  is  the  anhydride  of  gallic  acid.  When  an 
aqueous  solution  of  tannic  acid  is  allowed  to  remain  ex- 
posed to  the  air,  a  process  of  fermentation  takes  place  and 
it  is  converted  into  gallic  acid.  A  number  of  other  tan- 
nic acids,  and  also  gallic  acid  itself,  are  used  in  the  manu- 
facture of  inks. 

295.  Iron  Inks.  —  When  a  water  solution  of  pure  ferrous 
sulphate  is  added  to  a  water  solution  of  tannic  acid,  a  color- 
less solution  results  (Fig.  93,  a).  If  this  colorless  solution 
is  brought  in  contact  with  an  oxidizing  agent,  for  example, 
hydrogen  peroxide,  the  fluid  immediately  changes  to  a 


FIG.  92.  —  NUTGALLS,  ACTUAL  SIZE. 


316 


INK 


black  color.  This  change  is  due  to  the  fact  that  while  the 
ferrous  salts  of  the  tannic  acids  are  soluble  in  water,  the 
ferric  salts  of  many  of  them  are  black  and  insoluble. 
When  the  colorless  solution  referred  to  above  is  exposed 
to  air,  oxidation  takes  place  slowly  (Fig.  98,  6),  and  the 
consequent  blackening  occurs  less  rapidly.  This  slow 
oxidation  may  be  further  hindered  by  the  addition  of  a 
few  drops  of  some  strong  acid,  for  example,  sulphuric  acid. 
When  a  solution  of  ferrous  tannate  is  used  as  an  ink,  the 

writing  is  at  first  nearly  in- 
visible, but  on  exposure  to  air, 
oxidation  takes  place  and  the 
writing  becomes  black.  In 
order  that  the  writing  may  be 
visible  when  the  ink  is  first  ap- 
plied to  the  paper,  some  pig- 
ment, such  as  indigo  carmine, 
is  added  to  the  ink.  This  gives 
ink  a  blue-black  color  when 
first  applied,  and  this  color  is 
later  changed  to  black  by  the 
oxidation  of  the  ferrous  tannate. 
To  cause  the  ink  to  adhere  to 
the  pen  and  thus  prevent  blot- 
ting, some  mucilaginous  substance  is  added,  for  example, 
dextrin  or  gum  arabic.  As  the  ink  would  be  likely  to 
mold  on  being  exposed  to  the  air,  a  small  quantity  of 
some  fungicide,  such  as  carbolic  acid,  is  used  to  kill  the 
germs  that  may  fall  into  the  ink  from  the  air. 

296.  Logwood  Inks.  —  Logwood,  or  campeachy  wood,  as  it 
occurs  in  the  market,  consists  of  chips  of  the  campeachy 
tree  which  grows  in  Mexico,  Central  America,  and  the 
West  Indies.  When  boiled  in  water,  a  dye  is  extracted 


FIG.    93.  —  FERROUS    TANNATE 
INK  OXIDIZED  BY  AIR. 


INDIA   INKS  317 

from  logwood  which  has  long  been  used  to  improve  the 
quality  of  gall -inks.  Potassium  chromate  when  added  to 
logwood  extract  obtained  in  the  manner  just  mentioned 
yields  a  black  fluid;  ferrous  and  copper  salts  yield  dark 
colored  fluids  that  oxidize  more  slowly  than  gall  inks. 

297.  Nigrosin  Inks.  —  Nigrosin  is  an  anilina  dye  -exten- 
sively employed  for  the  preparation  of  cheap  inks.    Various 
grades  of  nigrosin  are  on  the  market,  and  for  this  reason 
nigrosin  inks  vary  considerably.     In  some  cases  the  color- 
ing matter  is  not  in  solution  and  much  of  it  settles  as  a 
thick  mud  in  the  inkwell.     It  is  impossible  to  obtain  good 
results  by  writing  with  a  pen  covered  with  this  thick 
deposit.     A  good  grade  of  nigrosin  is  soluble  in  water  and 
yields  a  good  ink  for  temporary  use.     The  color  is  never 
black;  it  fades  in  a  comparatively  short  time,  and  may  be 
readily  removed  by  washing  in  water  or  in  a  dilute  solu- 
tion of  ammonium  hydroxide. 

298.  India  Inks.  —  Very  pure,  finely  divided  carbon,  in 
the  form  of  specially  prepared  lampblack,  forms  the  basis 
of  India  inks.     This  is  often  made  into  small  cakes  by  the 
use  of  some  binder  such  as  gum  arabic  or  glue.     When 
needed  for  use,  a  small  portion  of  the  cake  is  dissolved  in 
water.     There  are  also  various  fluid  inks  that  contain 
finely    divided  carbon,  held   in  suspension  by  a  suitable 
vehicle.     Such  inks  produce  a  permanent  black  and  are 
not  attacked  by  chemicals.     Sometimes  the  ink  is  held  to 
the  paper  by  some  adhesive  material  that  deteriorates,  so 
that  in  the  course  of  time  the  pigment  can  be  easily  rubbed 
off.     The  only  way  in  which  spots  of  carbon  ink  can  be 
removed  is  to  make  use  of  some  liquid  that  will  dissolve 
the  binding  material  which  holds   the  carbon  to  the  paper 
or  cloth.     Carbon  tetrachloride  will  in  many  instances  do 
this. 


318  INK 

299.  Sepia  is  a  pigment,  varying  from  brown  to  black, 
secreted  by  several  species  of  cephalopods,  including  the 
common  cuttlefish.     This  pigment  is  discharged  by  the 
animal  into  the  water,  in  order  to  darken  it  and  make 
possible  an  escape  from  an  enemy.     The  pigment  of  the 
cuttlefish  was  one  of  the  early  inks  and  is  believed  to 
have   been  used  by  the  Romans.     At  the  present  time, 
the  dried  ink  sacks  of  the  cuttlefish  are  an  article  of 
commerce.     The  pigment  is  obtained  by  boiling  the  pul- 
verized sacks  with  lye ;  neutralizing  the  lye  with  acid  in 
order  to  precipitate  the  pigment ;    thoroughly  washing  the 
pigment  with  water  and  drying  at  a  low  temperature.    The 
resulting  material  forms  the  base  of  the  sepia  used  by  artists. 

300.  Red  Inks.  —  A  great  variety  of  red  inks  are  offered 
for  sale.     The  older  varieties  are  ammoniacal  solutions  of 
the  pigment  of  the  cochineal  insect,  or  an  acetic  acid  solu- 
tion of  the  dyestuff,  Brazil-wood.     The  cochineal  insect  is 
a  bug  that  lives  on  several  species  of  cactus,  one  of  which 
is  cultivated  for  this  purpose  in  Mexico,  Central  America, 
and  several  warm  countries  of  the  far  east.     The  cochineal 
bugs  of   commerce  are  the  dried   remains  of  the  female 
cochineal  insect.     After  the  females  have  deposited  their 
eggs,  they  are  killed  by  steam  or  hot  water,  or  by  spread- 
ing them  on  heated  plates.     Those  prepared  by  the  latter 
method  are  considered  superior  for  use  in  making   ink. 
Pure  carmine  is  the  pigment  obtained  from  the  cochineal 
insect  and  is  soluble  in  water,  but  the  name  carmine  has 
been  given  also  to  several  colors  derived  from  the  pigment 
of  cochineal. 

Quite  a  variety  of  aniline  colors,  such  as  eosine  and 
ponceau  scarlet,  form  the  base  of  most  of  the  modern  red 
inks.  Water  glass  is  used  in  the  manufacture  of  water- 
proof red  inks. 


PRINTERS'  INK  319 

It  is  necessary  to  have  some  knowledge  of  the  composi- 
tion of  a  red  ink  in  order  to  remove  it  from  cloth.  Some 
of  the  pigments  used  are  very  difficult  to  bleach.  Carmine 
and  cosine  are  readily  destroyed  by  chlorine.  Chlorine 
should  never  be  liberated  in  contact  with  silk  or  woolen 
goods. 

301.  Copying  Inks.  —  The  demand  for  copying  inks  has 
greatly  decreased  since  the  introduction  of  the  typewriter 
and  carbon  paper.     When,  however,  it  is  desirable  to  retain 
a  copy  of  a  letter  written  with  a  pen,  it  is  usually  made  by 
placing  the  original  beneath  the  moistened  page  of  a  letter 
book  and  then,  by  means  of  a  press,  forcing  the  two  firmly 
together.     A  portion  of  the  ink  enters  the  thin  page  of 
the  letter  book,  and  an  exact  copy  of  the  letter  is  obtained. 
A  good  copying  ink  must  not  harden  rapidly  and  should 
possess  a  considerable  body.     These  qualities  are  secured 
by  the  addition  of  some  slightly  hygroscopic  substance, 
such  as  sugar,  dextrin,  or  glucose,  to  ordinary  ink.     Copy- 
ing inks  of  excellent  quality  are  on  the  market  and  are 
inexpensive. 

302.  Printers'  Ink  is  usually  a  thick  linseed  oil  varnish 
to  which  soap  and  finely  divided  carbon  have  been  added. 
The  varnish  is  obtained  by  heating  linseed  oil  until  the 
more  volatile  portions  of  the  oil  are  driven  off,  and  a  thick 
liquid  remains  which  can  be  drawn  out  in  long  filaments. 
The  lampblack  is  then   incorporated.     Soap  is  added  to 
the  better  grades  of  ink  to  prevent  the  type  from  adhering 
so  firmly  to  the  ink  that  the  print  will  be  smeared  when 
the  paper  and  type  separate.     In  the  cheaper  grades  of 
ink,  long  continued  boiling  is  obviated  by  the  addition  of 
rosin,  and  linseed  oil  may  be  replaced  by  a  less  expensive 
material,  such  as  rosin  oil  or  nut  oil. 


320  \INK 

SUMMARY 

Black  Writing  Inks  depend  for  their  color  upon  one  of  the  fol- 
lowing: (a)  the  formation  of  ferric  tannate,  (b)  an  aniline  dye, 
generally  nigrosin,  (c)  finely  divided  carbon,  usually  in  the  form 
of  lampblack. 

The  Tannic  and  Gallic  Acids  used  in  the  manufacture  of  inks  are 
obtained  chiefly  from  nutgalls,  which  are  morbid  growths  produced 
on  the  twigs  of  oak  trees  by  gall-flies. 

Iron  Inks  are  water  solutions  of  iron  salts  of  tannic  and  gallic 
acids  to  which  have  been  added  (a)  a  dye  to  make  the  ink  visible 
when  first  used,  (b)  a  mucilaginous  substance  to  cause  the  ink 
to  better  adhere  to  the  pen,  (c)  a  preservative  to  prevent  the 
growth  of  fungi  in  the  ink. 

Iron  Ink  Spots  may  be  removed  from  white  cotton  or  linen 
goods  by  the  following  course  of  procedure  : .  (a)  the  reduction  of 
insoluble  ferric  tannate  to  soluble  ferrous  tannate,  (b)  washing  in 
water,  (c)  bleaching  the  temporary  color,  (d]  careful  removal  of 
the  bleach. 

Nigrosin  Inks  are  water  solutions  of  nigrosin.  They  are  neither 
black  nor  permanent,  and  can  be  removed  by  washing. 

India  Inks  depend  upon  finely  divided  carbon  for  their  color. 
The  carbon  is  held  in  suspension  by  a  suitable  vehicle  which  con- 
tains a  binder  to  hold  the  carbon  to  the  paper.  Carbon  is  the 
most  durable  pigment  used  in  the  manufacture  of  ink.  The  per- 
manence of  an  India  ink  depends  upon  the  adhesive  nature  and 
the  lasting  qualities  of  the  binder. 

Sepia  Inks  are  made  from  a  pigment  secreted  by  cuttlefish. 
They  are  among  the  most  durable  of  inks. 

Red  Inks  vary  greatly  in  composition.  The  pigment  used  in 
making  a  red  ink  may  be  obtained  from  the  cochineal  insect  or 
from  Brazil-wood,  or  it  may  be  one  of  the  soluble  synthetic  dyes. 

Copying  Inks  contain  some  slightly  hygroscopic  substance  in 
addition  to  the  materials  used  in  making  an  ordinary  ink. 


EXERCISES  321 

Printers'  Ink  is  a  carbon  ink  and  the  vehicle  is  generally  a 
linseed  oil  varnish. 

The  Removal  of  Ink  Spots  from  colored  cloth  and  from  white 
silk  and  woolen  goods  without  injury  to  the  fabric  is  difficult  and 
often  impossible. 

EXERCISES 

1.  Mention  three  classes  of  black  writing  inks. 

2.  What  are  some  of  the  general  properties  of  the  tannins? 

3.  What  is  the  chief  source  of  the  tannic  and  gallic  acids 
used  in  the  manufacture  of  ink? 

4.  What  causes  nutgalls  to  form  ? 

5.  What  relation  does  tannic  acid  bear  to  gallic  acid  ? 

6.  Briefly  state  the  principles  upon  which  the  manufacture 
of  an  iron  ink  is  based. 

7.  Why  does  a  mild  reducing  agent  such  as  milk  aid  in 
the  removal  of  fresh  spots  of  an  iron  ink  from  clothing  ? 

8.  Compare  the  properties  of  a  nigrosin  ink  with  those  of 
an  iron  ink. 

9.  What  is  the  pigment  used  in  making  India  ink  ? 

10.  Upon  what  does  the  durability  of  India  ink  depend  ? 

11.  What  are  sepia  inks  ?     How  do  the  colors  of  sepia  inks 
compare  with  the  color  of  a  carbon  ink  ? 

12.  Name  some  of  the  pigments  used  in  the  manufacture  of 
red  ink. 

13.  What  is  pure  carmine  ?     Of  what  do  most  of  the  car- 
mines on  the  market  consist  ? 

14.  Why  is  it  generally  more    difficult   to   determine  the 
course  of  procedure  for  the  removal  of  red  ink  spots  than  for 
the  removal  of  black  ink  spots  from  cotton  goods  ? 

15.  How  do  copying  inks  differ  from  ordinary  inks  ? 

16.  Briefly  state  the  composition  of  a  good  quality  of  print- 
ers' ink. 


CHAPTER   XXVIII 


TEXTILE  MATERIALS 

303.  Plant  and  Animal  Fibers.  —  Cotton,  linen,  wool,  and 
silk  are  the  materials  from  which  the  various  fabrics  used 
in  the  home  are  commonly  woven.  Cotton  is  the  seed 
hairs  of  the  cotton  plant.  Linen  is  made  from  the  fiber 
of  the  flax  plant,  and  to  a  less  extent  from  hemp.  Jute, 
the  bast  fibers  of  the  jute  plant,  which  grows  chiefly  in 
India  and  Ceylon,  is  employed  to  some  extent  as  a  cheap 


Cotton 
FIG.  94. 


Cf 

Wool  Silk  Flax 

IMPORTANT  TEXTILE  FIBERS.     (Highly  Magnified.) 


substitute  for  linen.  The  term  wool,  when  used  in  a 
broad  sense,  refers  to  any  animal  hair  which  is  sufficiently 
fine  and  long  to  be  made  into  a  thread  that  can  be  woven 
into  cloth  suitable  for  use  as  clothing.  The  term  woolen 
goods  includes  not  only  the  cloth  made  from  the  hair  of 
the  sheep,  but  alpaca,  cashmere,  and  mohair,  as  well. 
Alpaca  is  made  from  the  fine  hair  of  the  fleece  of  the 
llama.  Cashmere  is  made  from  the  wool  of  the  Thibet 
goat.  Mohair  is  woven  from  the  fine  hair  of  the  Angora 

322 


I  CELLULOSE  323 

goat.  Silk  is  manufactured  from  the  thread  spun  by  sev- 
eral species  of  caterpillars  to  form  the  cocoons  in  which 
they  undergo  their  transformations  into  moths.  Practi- 
cally all  silk  is  obtained  from  the  cocoons  of  the  silkworm. 
The  chief  constituent  of  all  vegetable  fiber  is  cellulose, 
a  compound  that  is  of  the  greatest  importance,  not  only 
on  account  of  its  extensive  use  in  the  textile  "industries, 
but  on  account  of  the  enormous  quantities  employed  in 
the  manufacture  of  paper,  and  in  the  nitrocellulose  indus- 
tries (Chapter  XX). 

304.  Cotton.  —  Raw   cotton   fiber    contains  about  91  % 
of  cellulose,  the  remaining   9%   being  chiefly  water,  to- 
gether  with   small  quantities  of   fatty  and   nitrogenous 
substances.     A  cotton  seed-hair   is    a   single   plant   cell, 
tubular  in  shape,  which,  during  the  growth  of  the  plant, 
is  filled  with  liquid  protoplasm.     As  the  seed  ripens,  the 
protoplasm  disappears,  the  tube  collapses,  and  the  hair 
takes  a  twist  in  the  form  of  a  spiral.     This  latter  struc- 
ture is  characteristic  of  cotton  and  aids  in  the  spinning  of 
a  thread  from  the  seed-hairs.     There  are  several  species  of 
cotton ;  that  known  to  the  trade  as  Sea  Island  cotton  pro- 
duces the  longest  and  finest  seed-hairs,  and  commands  the 
highest  price. 

305.  Cellulose.  —  Very  pure   cellulose  can   be   obtained 
from  raw  cotton  by  boiling  it  in  an  alkali,  such  as  a  solu- 
tion of  sodium  carbonate,  or  a  dilute  solution  of  sodium 
hydroxide  ;  rinsing  first  with  water  and  then  with  a  dilute 
solution  of  an  acid ;  thoroughly  washing  and  finally  dry- 
ing.     From    a   chemical   standpoint,    cellulose   possesses 
both  weak  acidic  and  weak   basic   properties.      Neither 
acid  nor  basic    dyes  adhere    to  pure  cotton   fiber.     The 
chemical  nature  of  cellulose  is  utilized  in  making  mercer- 
ized cotton  and  several  varieties  of  artificial  silk. 


324 


TEXTILE  MATERIALS 


306.  Mercerized  Cotton  was  named  for  John  Mercer  who, 
in  1844,  first  published  the  principles  of  its  manufacture. 
When  cotton  is  treated  with  a  concentrated  solution  of 


Copyright  by  Underwood  &  Underwood,  N.  Y. 

FIG.  95.  —  PART  OF  THE  4,000,000  BALES  OF  THE  YEARLY  TEXAN 
COTTON  CROP. 


sodium  hydroxide,  it  contracts  to  about  three  fourths  of 
its  original  length,  and  is  converted  into  a  new  substance 
called  alkali  cellulose.  If  the  alkali  cellulose  is  now 


CHARDONNET  SILK  325 

stretched  to  the  length  of  the  original  cotton,  and  then 
thoroughly  washed,  it  is  changed  to  cellulose  hydrate,  and 
the  fiber  takes  on  a  silky  sheen.  The  best  results  are 
obtained  when  the  sodium  hydroxide  solution  contains 
from  27  %  to  32  %  of  caustic  soda,  and  is  used  at  a  tem- 
perature below  21°  C.  The  luster  is  greatly  affected  by 
the  tension  which  is  applied  simultaneously  with,  or  just 
after,  the  formation  of  the  alkali  cellulose.  Mercerized 
cotton  is  stronger  than  ordinary  cotton  and  has  a  greater 
affinity  for  dyes. 

307.  Artificial  Silks.  —  At  least  three  classes  of  silks  are 
made  from  cellulose,  namely,  pyroxylin  silks,  silks  made 
from  a  solution  of  cellulose  in  ammoniacal  cupric  oxide, 
and  those  made  from  viscose. 

308.  Chardonnet  Silk  was  named  for  Count  Hilaire  de 
Chardonnet  who  perfected  a  process  for  its  manufacture. 
It  is  the  best  known  of  the  pyroxylin  silks. 

In  the  manufacture  of  Chardonnet  silk,  pure  cellulose 
is  converted  into  collodion,  which  is  forced  through 
fine  capillary  tubes  by  a  pressure  of  from  40  to  50  at- 
mospheres. As  soon  as  the  fine  threads  of  collodion 
come  in  contact  with  air,  they  solidify  and  can  be 
rolled  on  bobbins.  The  fine  threads  are  kept  moist 
until  after  the  formation  of  coarser  threads  suitable 
for  weaving.  The  coarser  threads  are  made  by  twist- 
ing together  from  12  to  20  of  the  finer  threads.  Since 
pyroxylin  is  very  inflammable,  it  is  not  suitable  for 
use  as  clothing  and  must  be  converted  into  a  substance 
much  less  easily  ignited.  This  is  brought  about  by 
treating  the  nitrocelluloses  with  some  substance,  for 
example,  a  solution  of  calcium  sulphide,  that  will 
change  the  nitrocelluloses  to  cellulose,  but  will  leave 


326  TEXTILE  MATERIALS 

the    cellulose    in   a    form    which    closely   resembles   silk 
in  appearance. 

309.  Pauly's  Silk. — In  making  artificial  silks  of  this  class, 
the  cellulose  is  either  dissolved  directly  in  a  cuprammo- 
nium  solution,  or  is  converted  into  alkali  cellulose  and 
then  dissolved. 

310.  Viscose  Silk.  —  Viscose  is  made  by  treating  cellu- 
lose, obtained  chiefly  from  wood,  with  a  sodium  hydroxide 
solution  and  then  adding  carbon  disulphide  to  the  soda 
cellulose    that  is  formed.     It  dissolves  readily  in   water 
and  the  water  solution  decomposes  when  exposed  to  air, 
yielding  cellulose  as  one  of  the  products  of  decomposition. 
Viscose  is  so  unstable  that  it  cannot  be  stored  and  trans- 
ported over  long  distances  unless  great  care  is  taken  to 
have  the  containers  tight  and  to  keep  the  temperature 
near  the  freezing  point  of  water.     Viscose,  or  rather  vis- 
coid,  the  precipitated  cellulose  obtained  from  it,  has  many 
uses.     It  is  employed  as  sizing  for  paper  and  as  a  substi- 
tute for  celluloid.     It  bids  fair  to  become  a  very  important 
substance  for  use  in  the  manufacture  of  artificial  silk,  or 
luster  cellulose. 

The  manufacture  of  viscose  silk  is  carried  on  essentially 
as  follows.  A  water  solution  of  viscose  is  filtered  to  free 
it  from  particles  of  solid  cellulose  that  would  clog  the  fine 
capillary  tubes  of  the  spinning  machine.  The  threads  are 
then  spun  in  the  usual  way,  but  after  leaving  the  spinning 
tubes  they  are  allowed  to  hang  so  as  to  be  stretched  by 
their  own  weight.  The  threads  are  then  rapidly  converted 
into  cellulose  by  means  of  currents  of  warm  air.  In  place 
of  air,  solutions  of  ammonium  chloride  and  of  ammonium 
sulphate  are  said  to  be  used  by  some  manufacturers  to 
convert  the  viscose  threads  into  cellulose.  There  are  a 


LINEN  327 

great  many  mechanical  difficulties  to  be  overcome  in  mak- 
ing viscose  threads  fine  enough  for  use  as  a  substitute  for 
silk.  In  spite  of  these  difficulties  a  viscose  product  scarcely 
to  be  distinguished  from  silk  is  on  the  market.  It  has  a 
more  brilliant  luster  than  silk,  compares  favorably  with 
it  in  strength,  and  seems  destined  to  enter  into  keen  com- 
petition with  the  genuine  article. 

311.  Linen  consists  of  bast  fibers,  chiefly  obtained  from 
flax.  Plants  that  are  gathered  before  the  seed  has  ripened 
yield  a  fiber  most  suitable  for  making  linen  thread. 
When  especially  fine  fiber  is  desired,  the  plants  are  raised 
under  conditions  that  cause  them  to  have  slender  stems. 
Plants  intended  for  the  production  of  linen  are  pulled, 
roots  and  all,  and  have  their  leaves  and  seed-pods  removed 
by  a  process  called  rippling ;  the  residue  is  known  as 
straw.  The  bast  fibers  are  separated  from  the  undesirable 
parts  of  the  straw  by  one  of  the  several  methods  termed 
retting.  The  natural  means  of  retting  consist  of  processes 
of  decay,  during  which  the  bast  fibers  are  thoroughly 
loosened.  Chemical  retting  involves  the  use  of  dilute 
sulphuric  or  hydrochloric  acid  solutions  and  requires  a 
much  shorter  time  than  the  natural  process.  After  the 
retting  is  complete,  the  flax  is  thoroughly  washed,  dried, 
and  then  submitted  to  mechanical  processes  that  free 
the  fibers  from  the  woody  tissue  and  make  them  into 
bundles  of  filaments  ready  for  spinning. 

Linen  is  not  pure  cellulose,  and  is  more  readily  disin- 
tegrated than  cotton  by  strong  alkalies  and  by  chlorine 
and  similar  oxidizing  agents.  The  differences  between 
the  shape  of  linen  fiber  and  of  cotton  fiber  as  revealed 
under  the  microscope  (Fig.  94),  furnishes  the  most  reli- 
able method  for  distinguishing  linen  from  cotton.  Old 
linen  that  has  been  laundered  many  times  is  practically 


328  TEXTILE  MATERIALS 

pure  cellulose  and  cannot  be  distinguished  from  cotton 
by  chemical  tests. 

312.  Wool  is  composed  of  nitrogenous  substances  con- 
taining sulphur.  Unwashed  wool,  in  addition  to  dirt  held 
mechanically  to  the  fiber,  contains  incrusting  matter  that 
consists  of  two  parts ;  one  soluble  in  water  (the  suint  or 
wool-perspiration),  and  the  other  soluble  in  fat  solvents 
(the  yolk  or  wool-fat).  Either  of  the  words  "suint"  or 
"  yolk  "  is  often  used  as  the  name  for  the  complete  incrust- 
ing material. 

Preparatory  to  being  made  into  yarn,  wool  is  freed  from 
dirt  and  the  incrusting  material.  This  may  be  accom- 
plished by  a  single  operation,  or  the  process  may  be 
divided  into  two  steps.  The  one-step  process  (scouring) 
is  accomplished  by  washing  the  wool  in  a  weakly  alkaline 
solution  of  soap,  or  by  the  use  of  dilute  solutions  of  such 
alkalies  as  ammonium  carbonate,  ammonium  hydroxide, 
and  sodium  carbonate.  The  wash  water  in  this  case  con- 
tains the  wool-grease  and  also  potassium  salts,  both  of 
which  are  valuable  substances.  For  this  1-eason,  the  wash 
water  is  sometimes  evaporated  to  dryness  and  then  cal- 
cined for  the  purpose  of  securing  the  potassium  in  the 
form  of  potassium  carbonate.  At  other  times,  the  sus- 
pended impurities  are  allowed  to  settle  and  then  sulphuric 
acid  is  added  to  the  warm  solution  to  decompose  the 
soaps  and  to  cause  the  oils  and  fats  to  rise  to  the  surface. 
Lanolin,  much  used  as  a  basis  for  salves  and  ointments,  is 
a  purified  wool-fat.  The  wool-grease  and  suint  are  also 
obtained  separately  by  making  use  of  the  fact  that  the 
wool-grease  is  soluble  in  fat  solvents  (benzine,  petro- 
leum, naphtha,  ether,  etc.)  while  suint  is  soluble  in 
water. 

Wool  is  readily  attacked  by  alkalies,  even  dilute  solu- 


SILK  329 

tions  of  sodium  hydroxide  causing  it  to  dissolve.  In  this 
respect,  it  is  in  marked  contrast  to  cotton.  On  the  other 
hand,  acids  affect  cotton  much  more  readily  than  they  do 
wool.  Dilute  solutions  of  the  mineral  acids  have  practi- 
cally no  effect  on  wool.  Practical  use  is  made  of  this 
fact  by  employing  solutions  of  sulphuric  acid  and  of 
aluminum  chloride  to  free  wool  from  burs  •  and  other 
vegetable  matter  that  have  become  entangled  in  it.  ,  When 
heated  in  the  presence  of  water,  the  aluminum  chloride 
reacts  with  the  water,  yielding  hydrochloric  acid,  which  at- 
tacks the  vegetable  fiber  so  that  it  falls  to  pieces  and  can 
be  washed  from  the  wool.  Concentrated  mineral  acids 
destroy  wool  fiber.  Wool  is  rather  sensitive  to  heat ; 
when  raised  to  100°  C.,  the  fiber  rapidly  becomes  brittle. 
Strong  oxidizing  agents,  such  as  chlorine,  attack  wool. 
Since  wool  is  very  hygroscopic,  this  fact  should  be  taken 
into  consideration  when  purchasing  it. 

313.  Silk  is  a  nitrogenous  substance  containing  no  sul- 
phur, differing  in  this  respect  from  wool.  The  prepa- 
ration of  silk  thread  involves  several  operations,  the  more 
important  of  which  will  be  referred  to  briefly.  The 
cocoons  (§  303)  are  soaked  in  warm  water  for  the  purpose 
of  softening  the  silk-glue  so  that  the  fiber  may  be  reeled. 
During  the  process  of  reeling,  two  threads  (composed  of 
from  4  to  10  fibers)  are  made  to  cross  so  that  their  rub- 
bing against  each  other  softens  the  silk-glue  and  causes  the 
fibers  to  adhere  in  the  form  of  solid  uniform  threads  of 
raw  silk.  Raw  silk  is  so  hygroscopic  that  it  will  absorb 
moisture  amounting  to  30  %  of  its  weight  and  yet  appear 
to  be  dry.  This  makes  it  desirable,  for  the  purpose  of 
trade,  to  determine  accurately  the  amount  of  water  con- 
tained in  a  lot  of  silk  to  be  purchased.  The  operation  of 
determining  the  amount  of  moisture  held  by  a  textile 

• 


330 


TEXTILE  MATERIALS 


Copyright  by  Underwood  &  Underwood,  N.  Y. 

FIG.  96.  —  DRYING  SILKWORM  COCOONS  IN  TURKEY. 


PROPERTIES  OF  SILK  331 

fiber  is  termed  conditioning ;  thus  we  speak  of  silk-con- 
ditioning, and  of  wool-conditioning. 

Raw  silk  has  a  harsh  feel  and  is  lacking  in  luster,  so, 
before  being  made  into  cloth,  it  is  subjected  to  treatment 
that  makes  it  soft  and  glossy.  This  consists  in  suspend- 
ing the  silk  in  a  warm  soap  solution  to  dissolve  at  least  a 
part  of  the  silk-glue,  rinsing  in  a  sodium  carbonate  solu- 
tion, and  then  wringing.  Two  or  three  soap  baths  are 
used  for  the  finest  quality  of  silk.  Hanks  of  this  are  tied 
in  several  places,  put  into  linen  bags,  and  boiled  in  a  soap 
solution  until  all  of  the  silk-glue  has  been  removed.  Such 
a  silk  has  about  70  %  of  the  weight  of  the  raw  silk  from 
which  it  was  made.  Ecru  silk  is  obtained  by  treating 
raw  silk  with  a  weak  soap  solution  until  from  2  %  to  5  % 
of  the  weight  of  the  raw  silk  has  been  removed,  then 
washing  it  and  frequently  bleaching  it  with  sulphur  diox- 
ide. Dilute  solutions  of  acetic  and  tannic  acids  when 
dried  on  silk  increase  its  luster  and  cause  it  to  rustle  when 
rubbed.  During  the  process  of  dyeing,  silk  is  frequently 
weighted,  that  is,  mordanted  with  iron  or  tin  salts  which 
form  deposits  on  the  fiber,  so  that  the  weight  of  the  goods 
is  often  doubled.  Weighted  silks  are  likely  to  crack. 

Silk  is  more  resistant  than  wool  to  the  action  of  alkalies, 
and  less  resistant  than  cotton.  Concentrated  hydro- 
chloric acid  rapidly  dissolves  silk,  which  differs  in  this  re- 
spect from  wool.  Oxidizing  agents,  such  as  chlorine  and 
hypochlorites,  attack  the  fiber  of  silk. 

314.  Bleaching.  —  The  differences  in  the  chemical  com- 
position of  the  various  textile  fibers  and  of  the  coloring 
materials  to  be  destroyed,  make  it  impossible  to  use  a  sin- 
gle method  for  bleaching  cotton,  linen,  wool,  and  silk. 
Cellulose  is  capable  of  withstanding  the  action  of  chlorine 
as  well  as  that  of  acid  and  of  alkaline  baths.  On  the 


332  TEXTILE  MATERIALS 

other  hand,  wool  and  silk  are  readily  destroyed  by  both 
chlorine  and  alkalies. 

315.  Bleaching  of  Cotton.  —  Oxygen,  derived  from  hypo- 
chlorous  acid,  and  by  the  action  of  chlorine  on  water  in 
the  presence  of  organic  matter,  is  practically  the  only 
substance  used  for  bleaching  cotton.     The  hypochlorous 
acid  and  chlorine  are  obtained  by  the  reaction  between 
acids  and  bleaching-powder,  a  substance  made  by  passing 
chlorine  over  slaked  lime.     Preparatory  to  bleaching,  cot- 
ton yarn  is  boiled  out  in  alkaline  solution  to  remove  the 
waxy  coating  from  the  fiber.     This  process  consists  in 
causing  a  hot  alkaline  solution  to  circulate  through  the 
yarn  in  a  closed  tank,  called  a  Icier.     After  being  boiled 
out,  the  yarn  in  the  kier  is  thoroughly  washed,  then  taken 
out  and  treated  with  a  cold,  dilute  solution  of  bleaching- 
powder  (chemie).     The  yarn  is  next  washed  and  soured, 
that  is,  treated  with  a  dilute  solution  of  sulphuric  or  of 
hydrochloric  acid,  or,  after  the  washing,  it  may  be  ex- 
posed for  some  time  to  the  carbon  dioxide  of  the  air.     The 
acids  in  general,  even  as  weak  a  one  as  carbonic  acid, 
react  with  the  bleaching-powder  retained  by  the  cotton 
fiber,  producing  hypochlorous  acid  and  free  chlorine.    The 
hypochlorous  acid  is  itself  an  oxidizing  agent,  and  the 
chlorine   liberates  oxygen   from    the  water  in  the  fiber. 
This  oxygen  destroys  the  coloring  matter  of  the  yarn. 
After  being  bleached,  the   yarn   is   thoroughly    washed, 
worked  in  a  soap  solution,  and  then  dried.     In  the  cases 
of  raw  cotton  fiber  and  cloth,  the  process  varies  consider- 
ably from  that  described  above,  but  the  principles  involved 
are  the  same. 

316.  Bleaching  of  Linen.  —  As  unbleached  linen  fiber  is 
not  pure  cellulose,  and  is  much  more  readily  attacked  by 
chlorine  than  cotton,  a  different  process  of  bleaching  is 


BLEACHING   OF   WOOL  333 

employed.  The  bleaching  of  linen  is  one  of  the  ancient 
industries,  and  the  old  method  is  still  practiced  to  a  lim- 
ited extent.  This  consists  of  steeping  the  material  to  be 
bleached  in  an  alkaline  solution,  exposing  it  out  of  doors 
on  the  grass,  meanwhile  sprinkling  it  from  time  to  time 
with  water.  It  is  then  dipped  in  buttermilk  and  washed 
with  soap  and  water.  All  of  this  is  a  tedious  pro- 
cess, often  requiring  several  months  for  its  completion. 
Shorter  processes  involving  the  use  of  alkalies,  chloride  of 
lime,  acids,  and  exposure  on  grass,  have  been  invented, 
but  great  care  must  be  exercised  not  to  unduly  weaken 
the  fiber  by  chlorine. 

317.  Bleaching  of  Wool  is  usually  accomplished  through 
the  agency  of  either  sulphurous  acid  or  sodium  peroxide. 
When  sulphurous  acid  is  employed,  the  wool  is  thoroughly 
scoured,  washed,  and  then  subjected  to  the  action  of  sul- 
phur dioxide  produced  by  the  burning  of  sulphur.     After 
being  bleached,  the  wool  is  rinsed  in  water  containing  a 
little  bluing.     A  bath  of  sodium  bisulphite,  followed  by 
one  of  dilute  sulphuric  acid,  is  also  used  to  produce  sul- 
phurous acid  in  contact  with  the  fiber. 

When  sodium  peroxide  is  sprinkled  into  a  bath  of 
dilute  sulphuric  acid,  hydrogen  peroxide. is  produced.  This 
readily  decomposes,  when  in  contact  with  organic  sub- 
stances, yielding  oxygen.  Since  strong  alkalies  rapidly 
destroy  wool,  it  is  essential  not  to  add  an  excess  of  sodium 
peroxide,  but,  as  the  bleaching  proceeds  much  more  rap- 
idly in  the  presence  of  alkalies,  the  bleaching  bath  is  gen- 
erally made  slightly  alkaline  by  the  use  of  some  weak 
alkali,  for  example,  borax. 

318.  Bleaching  of  Silk.  —  Silk  is  sufficiently  light  colored 
to  be  used  unbleached  for  most  purposes.     When  it  is  de- 
sirable to  destroy  the  light  yellow  shade  of  the  natural 


334  TEXTILE  MATERIALS 

article,  sulphurous  acid,  or  sodium  peroxide,  may  be  used 
as  in  the  case  of  wool.  A  cold  dilute  solution  of  a  mix- 
ture of  nitric  and  hydrochloric  acids  is  also  employed  to 
bleach  silk. 

SUMMARY 

Cotton  is  nearly  pure  cellulose.  . 

Cellulose  is  not  readily  attacked  by  dilute  acids  and  alkalies,  nor 
by  oxidizing  agents  such  as  chlorine.  It  is  converted  into  the 
nitrocelluloses  by  mixtures  of  concentrated  nitric  and  sulphuric 
acids. 

Artificial  Silks  consist  of  cellulose.  During  their  preparation, 
the  raw  material  is  treated  by  various  processes  which  impart  to 
the  finished  product  a  silky  sheen. 

Linen  is  made  from  the  bast  fibers  of  several  plants,  the  flax 
plant  being  its  chief  source.  It  is  not  as  pure  cellulose  as  cotton, 
and  is  much  more  readily  disintegrated  by  strong  alkalies  and  by 
chlorine.  The  microscopical  examination  of  the  structure  of  the 
fiber  furnishes  the  most  reliable  means  of  distinguishing  between 
cotton  and  linen  (Fig.  90). 

Wool  is  composed  of  nitrogenous  substances  containing  sulphur. 
It  readily  dissolves  in  hot  solutions  of  alkalies,  and  is  colored 
by  many  dyes  that  do  not  affect  cotton,  for  example,  picric  acid. 

Silk  is  a  nitrogenous  substance  containing  no  sulphur.  It  is 
more  resistant  than  wool  and  less  resistant  than  cotton  to  the 
action  of  alkalies.  Concentrated  hydrochloric  acid  rapidly  dis- 
solves silk. 

EXERCISES 

1.  What  percentage  of  raw  cotton  is  cellulose  ? 

2.  How  may  pure  cellulose  be  obtained  from  cotton  ? 

3.  How  is  mercerized  cotton  made  ? 


EXERCISES  335 

4.  Why  would  it  be  desirable  to  substitute  the  name  "  luster 
cellulose  "  for  «  artificial  silk  "  ? 

5.  Briefly  describe  a  process  for  making  artificial  silk. 

6.  From   the   bast   fibers   of  what  plant   is  linen   chiefly 
obtained  ? 

7.  Compare  the  microscopical  structure  of  linen  with  that 
of  cotton. 

8.  Why  is  it  much  more  difficult  to  distinguish  by  chemi- 
cal reactions  between  cotton  and  linen  that  has  been  laundered 
many  times  than  it  is  to  distinguish  between  cotton  and  un- 
bleached linen  ? 

9.  Why  is  it  difficult  to  bleach  linen  without  injury  to  the 
fiber? 

10.  Mention  two  valuable  by-products  obtained  during  the 
preparation  of  wool  for  weaving. 

11.  What  practical  application  is  made  of  the  fact  that  hy- 
drochloric acid  attacks  vegetable  matter  much  more  readily 
than  it  does  wool  ? 

12.  Explain  why  soap  containing  a  considerable  quantity  of 
free  alkali  should  not  be  used  in  washing  woolen  goods. 

13.  How    could   a   person    determine   by   a   chemical    test 
whether  a  piece  of  goods  was  pure  wool  or  a  mixture  of  wool 
and  cotton  ? 

14.  Why   should   not   woolen    goods   be    left   on  a   steam 
radiator  ? 

15.  How  does  wool  differ  from  silk  in  chemical  composition  ? 

16.  Tell  how  to  distinguish  between  silk  and  artificial  silk. 

17.  Why  should  bleaching  powder  never  be  used  to  remove 
a  stain  from  silk  ? 

18.  What  is  the  principal  compound  used  in  the  bleaching 
of  cotton  ? 

19.  What  are  the  bleaching  agents  employed  for  wool  and 
silk? 


.  CHAPTER  XXIX 

DYES   AND   DYEING 

319.  Modern  Dyes.  —  Each  year  the  number  of  persons 
engaged  in  using   their  own   handiwork  to  make   their 
homes  and  clothing  more  artistic  is  increasing.      Dyes, 
intelligently  selected  and  artistically  used,  furnish  a  valu- 
able and  inexpensive   means  of  increasing  the   pleasing 
appearance  of  the  home.     Modern  methods  of  dyeing  date 
from  the  discovery  of  mauve  by  Perkin  in  1856.     Since 
that  time  the  discoveries  of  other  dyestuffs  have  followed 
in  rapid  succession,  and  the  methods  of  dyeing  have  been 
greatly   simplified.      Pleasing    shades,  that   neither   fade 
when  exposed  to  the  action  of  sunlight  nor  are  removed 
during  the  process  of  washing  with  water  and  a  good  soap, 
can  be  obtained  on  small  quantities  of  cotton,  linen,  silk, 
wool,  or   mixed  goods.     The  chemistry  involved  in  the 
synthetic  preparation  of  dyes  is  complex,  and  the  chemical 
names  and  formulas  of  the  compounds  used  would  mean 
nothing  to  the  student  of   elementary  chemistry.     Dyes 
may,  however,  be  classified  so  that  those  placed  in  one 
group  will  be  suitable  for  use  in  coloring  certain  textiles. 
A  dye  may  give  excellent  results  when  used  with  wool  and 
be  worthless  for  use  with  cotton. 

320.  Direct  Dyes  for  Cotton.  —  A  few  years  ago  it  was 
thought  to  be  impossible  to  dye  cotton  and  linen  without 
the  use  of  some  substance,  called  a  mordant,  that  would 
hold  the  color  to  the  fiber.     Recently  quite  a  number  of 
dyes  have  been  discovered  that  adhere  to  cotton  and  linen, 


USE   OF  DIRECT  DYES  337 

and  some  of  them  possess  a  satisfactory  permanence.  A 
dealer  in  dyes  is  likely  to  assign  a  characteristic  name  of 
his  own  to  a  special  class  of  dyes,  so  we  find  such  names 
as  Dianil,  Diamine,  Naphthamine,  and  Benzo  used  by 
different  firms  to  indicate  direct  dyes  for  cotton.  These 
terms  take  the  part  of  a  family  name,  and  the  color  that 
of  the  given  name.  Dianil  Yellow,  Dianil -Fast  Blue, 
Dianil  Fast  Black ;  Naphthamine  Fast  Yellow,  Naphtha- 
mine  Fast  Blue,  and  Naphthamine  Direct  Black  are  direct 
yellow,  blue,  and  black  dyes  for  cotton.  Dyes  of  this  class 
are  not  only  used  to  color  vegetable  fibers,  of  which  cotton, 
linen,  and  paper  goods  are  made,  but  some  of  them  are  of 
great  value  for  the  dyeing  of  silk,  wool,  and  mixed  goods 
as  well.  The  list  of  direct  dyes  is  being  increased  rapidly, 
so  that  it  will  soon  be  possible  to  obtain  by  their  use  fast 
colors  of  almost  any  shade. 

321.  Use  of  Direct  Dyes.  —  The  application  of  direct  dyes 
is  so  simple  that  little  experience  is  necessary  for  obtain- 
ing a  uniform,  satisfactory  color.  The  preparation  of  the 
dye  bath  consists  in  dissolving  the  dye  in  a  little  hot 
water,  straining  the  concentrated  solution  through  fine 
muslin,  to  remove  any  particles  that  may  remain  undis- 
solved,  and  then  adding  the  solution  to  the  quantity  of 
water  required  for  the  bath.  In  order  to  increase  the 
amount  of  color  that  may  be  obtained  from  the  bath,  some 
sodium  salt,  such  as  common  salt,  sodium  sulphate,  or 
sodium  phosphate,  is  frequently  added  to  the  bath  to 
lessen  the  solubility  of  the  dye.  For  obtaining  a  uniform 
shade,  it  is  essential  that  the  goods  be  thoroughly  wet 
with  water  before  being  placed  in  the  bath,  and  that  they 
be  kept  in  motion  while  in  the  dye  bath,  so  as  to  expose 
every  part  of  the  goods  to  the  dye  for  the  same  length  of 
time.  The  bath  should  be  hot  before  the  goods  are 


338  DYES  AND  DYEING 

.  i 

placed  in  it,  and  should  be  rapidly  brought  to  the  boiling 
point  after  the  goods  are  added,  and  kept  boiling  until 
the  desired  shade  is  obtained.  After  being  taken  from 
the  bath,  the  goods  should  be  thoroughly  rinsed  with 
water  and  then  dried.  Neither  washing  soda,  strongly 
alkaline  soap,  nor  bleaching  powder  should  be  used  in 
washing  goods  whose  color  depends  upon  direct  dyes. 

322.  Direct  Developed  Dyes.  —  An  interesting  process  for 
obtaining  certain  colors  on  cotton  goods  consists  in  apply- 
ing a  direct  dye,  and  then  placing  the  colored  material 
in  a  very  dilute  bath  of  sodium  nitrite  and  hydrochloric 
acid.     After  rinsing,  the  goods  are  placed  in  a  bath  con- 
taining a  chemical  that  will  cause  a  color  entirely  different 
from  the  original  to  appear  on  the  goods. 

323.  Acid  Dyes.  — Dyes  belonging  to  this  class  of  colors 
are  sold  in  the  form  of  the  potassium,  ammonium,  and 
calcium  salts  of  the  color  acids.     From  one  of  these  salts 
the  color  acid  is  liberated  in  the  dye  bath  by  the  addition 
of  an  acid,  either  sulphuric,  acetic,  oxalic,  or  formic  acid 
being  commonly  employed  for  this  purpose. 

This  class  of  dyes  is  seldom  used  for  coloring  cotton, 
but  is  of  great  value  in  dyeing  animal  fibers,  which  in 
general  possess  sufficient  basic  properties  to  cause  them 
to  combine  with  the  free  color  acid.  Free  alkalies  quickly 
remove  acid  colors  from  the  fiber.  For  this  reason,  the 
goods  dyed  with  acid  dyes  fade  rapidly  when  washed  with 
laundry  soap  or  washing  powder.  The  acid  colors  are, 
as  a  class,  extremely  fast  when  exposed  to  light.  The 
properties  just  mentioned  make  acid  dyes  of  special  value 
for  coloring  wool,  silk,  leather,  and  feathers  when  the 
articles  made  from  them  are  not  intended  to  be  washed. 
Fast  Acid  Blue,  Palatine  Scarlet,  Acid  Yellow,  Cashmere 
Black,  and  Nero  Cyanine  Blue  are  examples  of  acid  colors. 


THE   SULPHUR  COLORS  339 

324.  Basic  Dyes.  —  Fuchsine,  methyl  violet,  methylene 
blue,  Bismarck  brown,  and  malachite  green  are  among  the 
common   basic   colors.     Members   of   this   class   of   dyes 
readily  form  salts  with  acids.     They  dye  silk  and  wool 
directly,  because  these  substances  possess  acid  as  well  as 
basic  properties.     In  order  to  have  a  basic  dye  adhere  to 
cotton  or  to  linen,  it  is  necessary  to  first  treat  the  fiber  with 
some  substance,  a  mordant  (from  the  Latin  mordeo,  to  bite), 
that  will  cling  to  the  goods  and  also  to  the  color.     The  mor- 
dant serves  as  a  bond  of  union  between  the  dye  and  the  fiber 
to  be  colored.     It  fixes  the  dye  so  that  it  cannot  be  washed 
from  the  goods.     Cellulose  fibers  are  treated  with  an  acid 
mordant  before  being  colored  by  basic  dyes.     Tannic  acid 
is  commonly  used  for  this  purpose,  and  is  fixed  on  the  fiber 
by  treatment  with  a  solution  of  tartar  emetic  before  the 
goods  are  placed  in  the  dye  bath.     The  process  of  mor- 
danting  greatly  increases  the  difficulty  of  obtaining  an 
even  shade,  as  considerable  skill  is  required  to  mordant 
the   goods   uniformly.     Straw,  raffia,  willow,  and   bark- 
tanned  leather  generally  contain  sufficient  tannic  acid  to 
fix  basic  dyes.     These  colors  may  also  be  used  as  direct 
dyes  for  artificial  silks  made  from  nitrocellulose. 

As  a  class,  basic  dyes  fade  rapidly  when  exposed  to 
light.  They  are  too  gaudy  to  be  generally  pleasing  to 
persons  of  refinement,  but  this  defect  can  be  readily  over- 
come by  adding  to  the  dye  bath  a  small  quantity  of  a 
complementary  color.  In  fact,  very  interesting  results 
may  be  obtained  by  mixing  dyes  of  different  colors. 

325.  The  Sulphur  Colors  are  prepared  by  the  action  of 
sodium  sulphide  on  various    organic  substances.     When 
goods  dyed  with  them  are  exposed  to   the  air,  pleasing 
shades  are  produced  that  do  not  fade  and  are  not  removed 
by  washing.     Since  the  sulphur  dyes  are  used  in  strongly 


340  DYES  AND  DYEING 

alkaline  baths,  and  because  hot  alkalies  readily  attack 
wool  and  silk,  these  colors  are  chiefly  used  with  cotton 
and  linen  goods.  Only  one  dye  bath  is  necessary,  the 
color  being  fixed  by  exposure  to  the  air.  The  sulphur 
colors  appear  on  the  market  under  the  class  names  of 
Thyogene,  Kyrogene,  Thion,  Pyrogene,  and  Kaligene. 

326.  The  Vat  Colors.  —  Indigo,  which  is  produced  by 
plants  belonging  to  the  genus  Indigofera,  was  the  original 
dye  of  this  class,  and  has  been  employed  for  many  cen- 
turies. One  of  the  greatest  triumphs  of  modern  science 
was  accomplished  when  chemists  prepared  indigo  arti- 
ficially, at  a  cost  which  enabled  the  synthetic  product  to 
compete  with  the  natural  article,  and  so  simplified  the 
method  for  its  application  that  it  could  be  used  conven- 
iently in  the  home.  These  discoveries  followed  the  scien- 
tific determination  of  the  chemical  constitution  of  indigo, 
and  of  chemical  changes  that  took  place  in  the  dye  bath. 

Indigo  occurs  in  the  form  of  an  insoluble  substance 
that  can  be  rendered  soluble  through  the  agency  of  re- 
ducing agents.  The  soluble  material  enters  the  fiber, 
and  on  exposure  to  the  air  becomes  converted  by  oxidation 
into  the  insoluble  color  compound.  At  the  present  time, 
large  color  manufacturers  place  the  reduced  indigo  on  the 
market  in  a  form  which  is  readily  soluble  in  an  alkaline 
bath  in  the  presence  of  a  small  quantity  of  a  reducing 
agent.  The  goods  are  placed  in  a  vat,  containing  the 
reduced  coloring  matter  in  solution,  and  stirred  until  they 
become  thoroughly  saturated.  They  are  then  passed 
through  a  wringer  several  times,  in  order  to  leave  the  dye 
evenly  distributed,  and  hung  so  as  to  expose  them  to  the 
oxidizing  action  of  the  air.  The  bath  is  used  either  cold 
or  lukewarm,  so  that  the  alkali  does  not  injure  wool  as 
much  as  it  would  if  hot.  After  the  color  has  developed, 


SUMMARY  341 

the  goods  are  carefully  washed  to  remove  the  alkali,  and 
then  boiled  in  a  soap  bath  to  remove  the  excess  of  dye. 

Recently,  dyes  which  are  applied  in  a  manner  similar 
to  indigo,  producing  colors  other  than  blue,  have  been 
placed  on  the  market.  These  colors  are  known  as  vat 
dyes  and  appear  under  the  class  names  Helindrone,  Algol, 
Indathrene,  Hydrone,  and  Ciba.  As  a  class,  vat  dyes 
furnish  the  most  satisfactory  fast  colors  yet  introduced. 

327.  Other  Classes  of  Dyes.  —  Classes  of  dyes  other  than 
those  mentioned,  such  as  the  mineral  dyes,  iron  buff,  chrome 
yellow,  and  Prussian  blue,  and  the  alizarine  dye,  Turkey 
red,  have  been  omitted,  as  they  are  far  more  difficult  to 
apply  than  those  described. 

328.   Synthetic  Dyes  compared  with  Vegetable  Colors. —  The 

basic  dyes  are,  in  general,  made  from  aniline  and  consti- 
tute the  true  aniline  colors.  It  is  unfortunate  that  this 
term  has  been  popularly  extended  to  include  all  dyes 
prepared  artificially.  Basic  dyes  were  the  first  colors  to 
fee  synthesized.  On  account  of  the  rapidity  with  which 
they  change  color  when  exposed  to  light,  the  opinion 
arose  that  all  synthetic  colors  faded  much  more  rapidly 
than  vegetable  dyes.  This  is  far  from  true ;  in  fact,  the 
fastest  colors  produced  in  any  age  are  found  among  the 
modern  synthetic  dyes,  and  their  range  of  color  far  ex- 
ceeds that  known  to  the  ancients. 


SUMMARY 

Direct  Dyes  produce  reasonably  fast  colors  on  textiles  without 
the  aid  of  mordants.  There  has  been  a  great  increase  in  the 
number  of  direct  dyes  for  cotton  and  they  are  rapidly  replacing 
the  basic  dyes.  Cotton  colored  by  a  direct  dye  should  not  be 
washed  in  alkaline  solutions. 


342  DYES  AND  DYEING 

Acid  Dyes  are  of  great  value  for  coloring  animal  fibers.  They 
are  fast  to  light  but  are  readily  removed  by  alkalies. 

Basic  Dyes  cannot  be  used  for  coloring  cotton  without  the  aid  of 
a  mordant,  though  they  are  direct  dyes  for  silk  and  wool.  They 
are  not  fast  to  light  and  yield  gaudy  colors. 

Sulphur  Colors  are  especially  adapted  for  the  dyeing  of  cotton 
and  linen.  They  produce  pleasing  shades,  fast  to  light  and  not 
removable  by  washing. 

Vat  Colors  are  rendered  soluble  by  reducing  agents  and  the 
color  is  developed  on  the  goods  by  the  oxidizing  action  of  the  air. 
The  best  known  vat  color  is  indigo,  an  ancient  and  highly  esteemed 
dye. 

EXERCISES 

1.  Why  is  it  desirable  to  increase  the  number  of  dyes  that 
can  be  conveniently  used  to  produce  fast  colors  on  small  quan- 
tities of  material  ? 

2.  What  are  some  of  the  advantages  to  be  derived  from 
the  use  of  direct  dyes  ? 

3.  Is  a  direct  dye  for  wool  always  a  direct  dye  for  cotton  ? 

4.  Why  is  a  sodium  salt  generally  added  to  a  dye  bath 
containing  a  direct  dye  for  cotton  ? 

5.  Why  should  the  material  to  be  colored  be  thoroughly 
wet  with  water  before  being  placed  in  the  dye  bath  ? 

6.  Why  is  it  essential  to  work  goods  constantly  while  they 
are  in  the  dye  bath  ? 

7.  What  is  the  meaning  of  "  direct  developed  dye  "  ? 

8.  For  coloring  what  classes  of  textiles  are  acid  dyes  chiefly 
used  ?     Why  ? 

9.  What  are  some  of  the  advantages  and  some  of  the  dis- 
advantages to  be  derived  from  the  use  of  acid  dyes  ? 

10.  Why  is  it  necessary  to  mordant  cotton  goods  that  are 
to  be  colored  by  basic  dyes  ? 


EXERCISES  343 

11.  To  what  textiles  are  the  sulphur  colors  best  suited  ? 

12.  What  may  be  said  concerning  the  permanency  of  the 
sulphur  colors  ? 

13.  What  is  meant  by  a  "  vat  color"  ? 

14.  Why  are  the  mineral  dyes  and  alizarine  less  used  than 
formerly  ? 

15.  How  did  the  incorrect  impression  arise  that  all  artificial 
dyes  are  less  fast  to  light  than  the  vegetable  colors  ? 


CHAPTER   XXX 

PHOTOGRAPHY 

329.  Chemical  Changes  produced  by  Light.  —  While   we 
are  familiar  with  the  fact  that  light  is  frequently  pro- 
duced in  chemical  action,  we  often  fail  to  realize  that  the 
converse   is   true.      Many  chemical  actions  are   induced 
by   light,  and  some   proceed  only  when  energy  can  be 
absorbed  in  the  form  of  light.     The  fading  of  many  dyes 
is  a  common  example  of  this  fact.     The  building  of  starch 
from  carbon  dioxide  and  water  in  the  leaves  of  plants 
occurs,  only  under  the  influence  of  sunlight,  which  supplies 
the  necessary  energy.     This  may  perhaps  be  considered  the 
most  important  of  all  chemical  actions,  since  all  life  depends 
upon  it.     Several  of  the  chemical  changes  produced  'by 
light  are  used  as  the  basis  of  photographic  processes. 

330.  Blue  Prints.  —  A  comparatively  simple  process  is 
that  employed  to  produce  blue  prints,  much  used  to  make 
copies  of  architect's  plans  and  engineer's  drawings,  and 
occasionally  for  photographs.     It  depends  on  two  simple 
chemical  facts,  which  are: 

(1)  that  ferric  salts  are  changed  to  ferrous  salts  by  light 
if  a  reducing  agent  is  present ; 

(2)  that   potassium    ferricyanide   reacts   with   ferrous 
salts,  producing  an  intensely  blue  substance,  Turnbull's 
blue.     We   may  write  equations   for  these   reactions   as 
follows: 

344 


TERMS   USED  IN  PHOTOGRAPHIC  PROCESSES     345 


2  FeGl3 

ferric 
chloride 

3FeCl 

ferrous 
chloride 


+ 


H2C204  —  ^ 

oxalic  acid 
(reducing  agent)     , 

2  K8Fe(CN)6 

potassium 
ferricyanide 


2  FeCla    +    2  HC1    +    2  CO 


ferrous 
chloride 


hydrochloric 
acid 


Fe8[Fe(CN)6]a 

Turnbull's 
blue 


carbon 
dioxide 

6  KC1 

potassium 
chloride 


Paper  on  which  blue  prints  are  to  be  made  is  coated 
with  a  mixture  that  will  allow  both  of  these  actions  to 
occur  simultaneously.  The  mixture  contains  ammonium 
ferric  citrate,  which  serves  the  double  purpose  of  fur- 
nishing the  iron  compound  and  the  reducing  material, 
which,  in  this  case,  is  the  citrate  radical  of  the  salt.  The 
other  constituent  is  potassium  ferricyanide.  Where  light 
strikes  such  paper  it  changes  color,  and  on  washing,  a 
pronounced  blue  color  is  produced.  At  the  same  time, 
unchanged  material  is  washed  away. 

331  .  Terms  used  in  Photographic  Processes.  —  For  the  com- 
plete photographic  process  four  classes  of  substances  are 
nearly  always  employed.  They  are  : 

(a)   the  sensitive  substance  ; 

(5)  the  sensitizer,  which  makes  the  action  of  the  light 
on  the  sensitive  substance  more  pronounced,  and  which 
does  this  by  combining  with  one  of  the  products  produced 
by  the  action  of  light; 

(c)  the  developer,  which  brings  out  or  exaggerates  the 
initial  action  of  light  ; 

(d)  the  fixer,  which  removes  substances  not  altered  by 
the  preceding  operations,  and  which  makes  the  plate  or 
print  inactive  to  further  influence  by  light,  and  therefore 
permanent. 

In  blue  prints,  the  ferric  salt  is  the  sensitive  substance, 
the  citrate  radical  is  the  sensitizer,  the  potassium  ferri- 
cyanide is  the  developer,  and  water  is  the  fixer. 


346  PHOTOGRAPHY 

332.  Silver  Plates.  —  The  great  proportion  of  all  photo- 
graphic operations  makes  use  of  the  fact  that  silver  bromide 
is  sensitive  to  light.  The  nature  of  the  change  that  takes 
place  is  not  well  known,  but  it  results  in  the  liberation  of 
an  amount  of  bromine  which  is  exceedingly  small,  even 


FIG.  97  A. — THE  PLATE  OR  NEGATIVE. 

after  a  long  period  of  exposure.  By  mixing  the  silver 
bromide  with  gelatin,  a  much  more  sensitive  combination 
is  obtained,  because  gelatin  is  a  strong  absorbent  of  bro- 
mine, and  therefore  aids  the  liberation  of  bromine  from 
the  silver  bromide.  In  this  way,  it  acts  as  a  sensitizer  for 
silver  bromide.  In  preparing  plates  for  use  in  cameras 
the  emulsion  of  silver  bromide  in  gelatin  is  spread  in  a 
thin  layer  on  sheets  of  glass  or  on  transparent  celluloid. 
These  are  exposed  to  the  image  that  is  formed  in  the 
camera,  and  the  sensitive  film  is  affected  in  varying  degrees 
by  the  spots  of  light  and  shade.  When  removed  from 
the  camera,  these  plates  show  no  change  to  the  eye.  But 
when  they  are  put  in  an  alkaline  solution  of  a  weak  reduc- 


SILVER  PLATES  347 

ing  agent,  the  effect  of  the  light  soon  becomes  apparent. 
Black  spots  appear  where  most  light  struck  the  plate,  and  a 
negative  picture  is  obtained  (Fig.  97 A).  The  explanation 
of  the  changes  is  as  follows.  It  is  supposed  that  the 
effect  of  the  momentary  exposure  which  forms  the  initial, 


FIG.  97  B. — THE  PRINT  OR  POSITIVE. 

invisible,  so-called  latent  image,  is  to  deposit  an  infinitesimal 
amount  of  silver. 

AgBr     — >-     Ag     4-     Br 

silver  bromide  silver  bromine 

The  solution  of  weak  reducing  agent  which  develops  the 
plate  acts  most  rapidly  on  those  spots  where  the  minute 
quantity  of  silver  has  been  deposited,  the  silver  acting  as 
a  catalytic  agent.  The  action  must  be  stopped  at  the 
point  where  a  clear  image  is  obtained,  otherwise  the  entire 
amount  of  silver  bromide  would  be  reduced,  and  an  entirely 
black  plate  obtained. 

AgBr     +     H     — >-     Ag     -f     HBr 

silver  hydrogen  silver         hydrobromic 

bromide  (any  reducing  agent)  acid 


348  PHOTOGRAPHY 

A,pt>nsiderable  number  of  different  substances  are  used  as 
jcrevelopers  for  silver  plates.  The  more  common  ones  are 
amiilpl,  eikonogen,  pyrogallic  acid,  ortol,  etc.  These 
are  all  complicated  organic  compounds.  They  are 
used  in  alkaline  solution  in  order  that  the  hydrobromic 
acid  that  is  formed  in  the  developing  action  shall  be 
neutralized. 

To  fix  a  silver  plate  it  is  only  necessary  to  dissolve  out 
the  silver  bromide  that  has  not  been  acted  upon  by  the 
developer.  A  suitable  solvent  is  found  in  sodium  thio- 
sulphate,  Na2S2O3,  ordinarily  called  "hypo."  Finally, 
thorough  washing  and  drying  complete  the  process,  and  a 
permanent  negative  is  obtained. 

333.  Prints.  —  From  one  negative  it  is  possible  to  obtain 
an  indefinite  number  of  positive  prints  (Fig.  97B).  The 
processes  are  essentially  the  same  as  in  making  the  negative. 
The  sensitive  substance  is  silver  bromide,  made  more  sen- 
sitive by  some  substance  such  as  gelatin,  or  albumen,  which 
also  serves  the  purposes  of  holding  the  bromide  to  the 
paper  and  of  giving  surface  texture  to  the  paper.  In  the 
varieties  of  paper  most  used  nowadays,  only  a  latent  image 
is  formed  during  the  exposure  under  the  negative,  and 
this  is  brought  out  by  the  reducing  action  of  the  developer, 
as  with  the  negative.  Fixing  is  accomplished  with  a  solu- 
tion of  "hypo."  Other  types  of  paper,  less  used  than 
formerly,  are  covered  with  a  mixture  that  contains  a 
developing  agent  as  well  as  the  sensitive  mixture.  Such 
papers  show  an  image  forming  visibly  during  the  exposure 
under  the  negative.  These  papers,  after  fixing,  have  an 
undesirable  color,  and  require  toning.  This  process  is  one 
of  simple  replacement.  The  print  is  immersed  in  a  solution 
of  gold  chloride  or  of  a  platinum  salt,  and  the  metallic 
silver  is  replaced  by  metallic  gold  or  platinum. 


COLOR  PHOTOGRAPHY  349 

3Ag     +     AuCl3    —*-     Au     +     3AgCl 

silver  gold  chloride  gold  silver  chloride 

Toning  also  makes  prints  more  permanent. 

334.  Actinic  Power.  —  Different  colors  affect  silver  bro- 
mide in  unequal  degree.     Blue  light  has  a  very  pronounced 
effect,  while   red   and   orange  have  almost  none.     It  is 
because  of  this  fact  that  we  develop  plates  in  red  or  orange 
light.     Also,  it  is  well  known  that  red  objects  appear  black 
in  a  photograph,   and   that   blue  appears  white.      Light 
which  does  not  affect  the  plate  is  called  non-actinic. 

Since  all  colors  do  not  have  the  same  actinic  power, 
ordinary  photographs  do  not  have  true  color  values.  To 
remedy  this  defect  it  is  necessary  to  interpose  color  screens 
between  the  object  and  the  plate,  thus  reducing  the  in- 
tensity of  the  more  actinic  colors,  or  to  employ  a  special 
variety  of  plates  called  orthochromatic.  These  are  like 
ordinary  plates  except  that  they  have  been  treated  with 
baths  of  certain  dyes.  In  some  manner  not  fully  under- 
stood, these  dyes  have  the  power  of  increasing  the  sensi- 
tiveness of  silver  bromide  for  light  of  their  own  color. 
Photographs  on  this  kind  of  plate  are  much  more  accurate 
in  their  representation  of  light  and  shade,  but  these  plates 
have  the  disadvantage  of  being  slower  than  the  ordinary 
variety. 

335.  Color  Photography.  —  Experimenters  have  endeav- 
ored for  many  years  to  perfect  a  process  by  which   the 
colors  of  nature  could  be  obtained  in  a  photograph.     The 
problem  has  been  one  of  physics  rather  than  chemistry, 
and  in  the  more  or  less  successful  methods  that  have  ap- 
peared, the  chemical  actions  employed  do  not  differ  mate- 
rially from  those  that  have  been  described. 

In  one  of  these  processes,  the  glass  plate  is  covered  with 


350  PHOTOGRAPHY 

an  extremely  thin  layer  of  starch  cells,  some  of  which  have 
been  stained  red,  others  green,  and  still  others  violet. 
These  are  present  in  such  proportion  that  the  mixture 
appears  white  to  the  eye.  The  cells  are  compressed  under 
heavy  pressure  until  the  plate  is  covered  with  a  very  thin 
transparent  layer,  which,  under  the  microscope,  would 
appear  to  be  made  up  of  dots  of  red,  green,  and  violet. 
On  this  layer,  an  orthochromatic  emulsion  of  gelatin  and 
silver  bromide  is  spread.  The  exposure  in  the  camera  is 
made  with  the  glass  side  of  the  plate  to  the  front,  so  that 
the  layer  of  stained  starch  cells  is  between  the  image  and 
the  silver  bromide  film. 

Since  each  colored  starch  cell  can  transmit  only  its  own 
color  of  light,  it  is  apparent  that  the  silver  bromide  be- 
hind each  red  cell  will  be  affected  only  by  the  red  in  that 
part  of  the  picture.  A  similar  thing  is  true  for  cells  of 
each  of  the  other  two  colors.  When  the  plate  is  de- 
veloped, therefore,  a  certain  amount  of  opaque  metallic 
silver  will  be  deposited  behind  those  red  cells  where  red 
light  fell  in  the  image,  behind  the  green  cells  where  green 
light  fell,  and  behind  violet  cells  where  violet  light  fell. 
But  this  is  just  the  reverse  of  the  condition  that  we  desire ; 
we  want  these  spots  to  be  transparent,  so  that  red  light 
will  come  through  in  the  red  parts  of  the  picture. 

Hence,  after  the  plate  has  been  developed  and  before  it 
has  been  fixed,  the  metallic  silver  must  be  dissolved  out,  and 
the  plate  then  returned  to  the  developing  bath  so  that  the 
unchanged  silver  bromide  will  be  turned  into  opaque 
metallic  silver.  The  effect  of  this  is  to  make  the  silver 
deposit  positive  instead  of  negative,  and  the  plate  will  now 
be  opaque  in  all  spots  except  where  red  light  passed  through 
red  cells,  green  light  through  green  cells,  and  violet 
light  through  violet  cells.  In  these  spots  the  plate  will 
be  transparent,  and  the  eye  looking  at  it  by  transmitted 


SUMMARY  351 

light,  will  fuse  the  minute  spots  of  color,  and  see  a  picture 
that  approximates  closely  to  the  beauty  of  nature. 

By  this  process  only  one  picture  can  be  obtained  from 
each  exposure  in  the  camera,  and  the  plate  must  be  viewed 
by  transmitted  light. 

SUMMARY  * 

Light  induces  some  chemical  changes  just  as  others  are  induced 
by  heat. 

Light-sensitive  Substances  are  not  uncommon.  Important  ones 
are  silver  compounds,  especially  silver  bromide,  and  ferric  salts. 
Silver  compounds  are  used  in  ordinary  photography,  ferric  salts  in 
blue  prints. 

A  Sensitizer  is  a  substance  used  to  increase  the  rapidity  of  the 
action  of  light.  In  ordinary  plates,  gelatin  serves  two  purposes. 
It  is  a  sensitizer,  and  it  holds  the  silver  bromide  to  the  plate.  It  acts 
by  absorbing  bromine,  one  of  the  products  of  the  action  of  light. 

A  Developer  is  used  to  bring  out  the  effect  of  the  light  on  the 
plate.  In  ordinary  photography,  this  initial  effect  is  not  visible  to 
the  eye.  For  silver  bromide  plates,  the  developer  is  an  alkaline 
solution  of  a  weak  reducing  agent. 

A  Fixer  is  a  substance  used  to  dissolve  sensitive  material  that 
has  not  been  affected  by  the  processes  of  exposure  and  develop- 
ment. It  makes  the  plate  permanent. 

Negatives  are  pictures  made  in  the  camera.  They  have  the 
light  and  dark  of  the  object  reversed. 

Prints  are  made  by  practically  the  same  chemical  processes 
as  those  used  to  produce  negatives. 

Toning  is  sometimes  used  to  obtain  more  pleasant  colors  than 
those  that  appear  in  the  untoned  print. 

Ordinary  photographs  do  not  give  correct  representations  of  light 
and  shade,  warm  colors  appearing  too  dark  and  the  cold  ones  too 
light.  Orthochromatic  plates  and  color  screens  partly  correct  this 
defect. 


352  PHOTOGRAPHY 

Plates  that  show  photographs  in  color  have  been  made  by  pro- 
ducing minute  spots  of  red,  green,  and  violet  on  a  plate  under  the 
gelatin-silver  bromide  emulsion,  and  causing  the  various  photo- 
graphic operations  to  blot  out  by  deposits  of  metallic  silver  those 
spots  which  should  not  appear  in  the  picture.  In  this  way  pic- 
tures are  obtained  showing  vividly  all  the  colors  of  nature. 

EXERCISES 

1.  What  happens  in  the  photosynthesis  of  starch  in  the 
leaves  of  plants? 

2.  Name  some  chemical  actions  that  are  caused  by  light. 

3.  What  is  the  sensitive  substance  in  blue-print  paper? 
What  sort  of  substance  is  needed  as  a  sensitizer  ?     Why  is 
blue-print  paper  both  developed  and  fixed  by  simple  washing  ? 

4.  Why  is  not  blue-print  paper  more  commonly  used  in 
producing  photographs  ? 

5.  What  is  the  effect  of  light  on  silver  bromide  ?    How  can 
the  action  be  made  more  rapid  ?     Explain  this  effect. 

6.  What  is  the  chemical  nature  of  the  developers  used  for 
silver  bromide  plates  ?     Why  should  the  developing  solution 
be  alkaline  ? 

7.  Why  are  the  darks  and  lights  of  the  object  reversed  in 
a  plate  that  has  been  exposed  in  a  camera  ? 

8.  What  is  the  dark  substance  in  a  photographic  negative  ? 

9.  Why  is  gelatin  used  in  making  photographic  plates  ? 

10.  Why  do  black  spots  appear  on  the  hands  when  silver 
compounds  have  been  handled  in  the  laboratory  ? 

11.  Why  can  plates  be  exposed  to  red  or  orange  light  in  the 
dark  room  during  the  operation  of  development  ? 

12.  Is  the  silver  deposit  that  is  finally  left  on  a  color-photog- 
raphy plate  in  the  nature  of  a  positive  or  a  negative  ?     Ex- 
plain. 

13.  Why   can   only   one   copy   of  a   color   photograph   be 
obtained? 


CHAPTER   XXXI 
PAINTS,  OILS,  AND  PIGMENTS 

336.  Purposes  served  by  Paints.  —  The  use  of  paints  finds 
its  origin  in  two,  widely  different  human  necessities.    His- 
torically the  more  important  of  these  is  the  need  of  surface 
decoration  which  is  displayed  by  even  the  most  primitive 
of   savages.      Civilization   has   developed  this  need  into 
the   various  arts  of  design  and  pictorial  representation. 
The  other  use  arises  from  the  fact  that  many  materials 
used  in  manufacturing  or  building  operations  are  subject 
to  rust  or  decay.     Paint  delays  this  destructive  tendency. 

337.  Nature  of  Paints.  —  Paints  always  contain  an  opaque 
solid  and  a  liquid  which  holds  the  solid  in  suspension 
while  the  paint  is  being  spread  on  a  surface  and  which 
causes  it  to  adhere  firmly  to  the  substance  that  it  covers. 
The  solid  is  called  the  pigment,  and  the  liquid  the  vehicle. 
Pigments  include  many  substances,  from  those  that  give 
the  fundamental  white  through  those  that  furnish  all  the 
wide  range  of   color  that  we  use.     Vehicles  are  mainly 
of  two  classes  :   (a)  oils  that  become  solid,  gum-like  sub- 
stances by  absorbing  oxygen  from  the  air,  (b)  water  that 
contains  adhesive  or  cement-forming  material. 

The  choice  of  pigment  and  vehicle  depends  entirely  on 
the  use  which  the  paint  is  to  serve.  If  it  is  to  cover  an 
outside*  surface,  exposed  to  rain  and  weather,  the  highest 
possible  degree  of  insolubility  and  chemical  resistance  to 
air,  light,  and  water  is  desirable,  in  both  pigment  and 
vehicle.  If,  on  the  other  hand,  it  is  for  inside  work,  such 

353 


354  PAINTS,   OILS,   AND  PIGMENTS 

as  covering  plaster  walls,  or  the  canvas  of  stage  scenery, 
glue  and  water  make  a  satisfactory  and  cheap  vehicle. 

WHITE  PIGMENTS 

In  white  pigments  the  important  qualities  are : 

(a)  high  covering  power,  tested  by  ascertaining  how 

much  black  surface  a  given  weight  or  a  given  volume  will 

cover  ; 

(&)  durability  ; 

(c)  ability  to  combine  well  with  linseed  oil  ; 

(d)  pure  whiteness  of  color  as  opposed  to  gray  or  yel- 
low tinges  ; 

(e)  ease  of  application  with  the  brush. 

338.  White  Lead.  —  Until  fifty  or  sixty  years  ago  the 
only  white  pigment  in  use  was  white  lead.  This  sub- 
stance is  a  basic  carbonate  which  we  may  describe  as  a 
mixture  of  lead  hydroxide  and  lead  carbonate,  represented 
by  the  formula  Pb(OH)2  •  2  PbCO3.  This  contains  31  % 
of  lead  hydroxide  and  69  %  of  lead  carbonate.  The  lead 
hydroxide  appears  to  react  with  linseed  oil,  which  is  most 
frequently  used  as  a  vehicle,  forming  a  smooth,  easily 

worked  substance.    A  high 

per  cent  of  the  hydroxide 
is  desirable. 

The  oldest  process  for 
making  white  lead  is  known 
as  the  Dutch  process.  It 
is  still  used  and  more 
white  lead  is  produced  by 
FIG.  98.  it  than  by  all  other  pro- 

cesses   combined.      Lead 

disks  are  placed  in  earthen  pots  that  contain  a  little  dilute 
acetic  acid  (Fig.  98);  the  pots,  many  in  number,  are  piled 


ZINC   OXIDE  355 

in  tiers,  and  embedded  in  tan  bark,  in  such  a  way  that  a 
draft  of  air  continually  flows  over  them.  The  tan  bark 
ferments,  producing  carbon  dioxide  and  causing  an  eleva- 
tion of  temperature.  After  some  90  days,  the  action  is 
completed.  The  long  period  of  the  action  is  the  chief 
objection  to  the  process,  and  is  a  reason  for  the  search  for 
other  methods.  Several  of  these  are  in  operation.  One 
of  them  hastens  the  action  by  using  lead  that  is  in  a  finely 
divided  or  "  atomized  "  condition.  In  another,  electroly- 
sis is  employed ;  but  none  of  them  have  as  yet  succeeded 
in  displacing  the  old  process. 

339.  Sublimed  White  Lead.  —  This  is  a  valuable  white 
pigment  that  has  come  into  use  in  recent  years.     It   is 
obtained  by  the  direct  heating  of  galena  (lead  sulphide, 
PbS),  and  consists  approximately  of  75  %  lead  sulphate, 
20  %  lead  oxide,  and  5  %  zinc  oxide.     It  is  more  durable 
than  white  lead  when  exposed  to  sea  air.     When  mixed 
with   linseed   oil  it   hardens  (dries)  rapidly,    and    forms 
a  tough,  impervious  coating. 

Other  zinc-containing  lead  whites  may  contain  zinc  oxide 
up  to  50  %.  One  of  these,  known  as  "  standard  zinc 
white,"  is  made  by  mixing  galena  and  zinc  sulphide  ores 
and  obtaining  from  them  a  volatile  product  at  a  high 
temperature.  This  consists  mainly  of  zinc  oxide  and  lead 
sulphate.  The  heat  causes  a  union  between  the  lead  sul- 
phate and  zinc  oxide  that  could  not  be  obtained  by 
mechanical  means. 

340.  Zinc  Oxide  is  a  pigment  which  is  rapidly  advancing 
into  favor,  particularly  when  mixed  with  ojbher  substances. 
A  combination  of  white  lead  and  zinc  oxide,  for  example, 
gives  a  paint  that  is  satisfactory  for  many  purposes,  since 
each  constituent  tends  to  balance  the  disadvantages  of  the 
other.     White  lead  tends  to  become  chalky  when  exposed 


356  PAINTS,    OILS,   AND  PIGMENTS 

to  light  and  weather,  while  zinc  oxide  remains  hard. 
Zinc  oxide,  on  the  other  hand,  tends  to  become  brittle,  to 
crack  and  peel,  while  white  lead  forms  a  tougher  coating. 
Zinc  oxide  is  made  by  heating  the  metal  in  air  or  by 
treating  its  ores  in  a  similar  manner. 

341.  Lithophone.  —  This   new   pigment,    which   is    also 
known  under  various  other  trade  names,  such  as  oleum 
white,  Beckton  white,  ponolith,  etc.,  is  made  by  mixing 
solutions  of  zinc  sulphate  and  barium  sulphide  : 

ZnSO4  +  BaS  — >-  BaSO4  +  ZnS 

zinc  barium  barium  zinc 

sulphate        sulphide  sulphate        sulphide 

Both  of  the  products  are  insoluble  in  water.  If  the  mix- 
ture of  precipitates  is  heated  to  dull  redness  and  plunged 
into  cold  water,  then  ground,  a  pigment  is  obtained  that 
is  brilliantly  white,  fine  in  texture,  and  of  good  covering 
power.  It  has  the  disadvantage,  however,  of  discoloring 
when  exposed  to  strong  sunlight. 

342.  Inert  Pigments.  —  These   are   used   as  diluents   or 
extenders,  and   are,  in   a   sense,  adulterants,   since   they 
diminish  the  covering  power  of  the  paint  and  the  ease  of 
its  application.     Many  of  them,  however,  give  increased 
durability,  and  they  are  much  used  in  ready-mixed  paints. 
Both  the  government  and  large    corporations    allow  the 
use  of  extenders  in  considerable  amounts.     In    view   of 
this  fact,  we  can  scarcely  consider  their  use  an  adultera- 
tion in  the  making  of  ready-mixed  paints. 

The  compounds  most  frequently  used  as  diluents  or 
fillers  are  :  silica  in  various  forms,  China  clay,  barium  sul- 
phate (barytes),  calcium  carbonate  in  the  form  of  whit- 
ing or  very  finely  ground  marble,  and  hyd rated  calcium 
sulphate  (gypsum).  Each  of  these  has  its  especial  advan- 


RED  PIGMENTS  357 

tage  of  cheapness  or  other  merit.  Silica  produces  a  sur- 
face that  wears  well  and  can  be  readily  repainted.  It  is 
claimed  that  barium  sulphate  and  gypsum  especially  in- 
crease the  wearing  qualities.  The  Pennsylvania  Railroad 
has  allowed  as  much  as  70  %  of  gypsum  in  its  car  paint. 

COLORED  PIGMENTS  9 

343.  The  Nature  of  Colored  Pigments.  — The  body  of  a 
paint  is  usually  a  white  pigment  which  serves  as  a  paint 
base  and  does  the  greater  part  of  the  covering.     But  if 
color  is  desired,  some  substance  of  high  coloring  power 
is  added.     This  substance  should  possess,  like  the  white 
pigment,  the  fundamental  characteristics  of  permanency, 
insolubility,  opaqueness,    and   covering   power.     Colored 
pigments  are  usually  metallic  oxides,  sulphides,  or  other 
insoluble  salts.     Occasionally  pigments  are  metallic   de- 
rivatives of  organic  dyes  ;  these  are  termed  lakes.     As  a 
rule,  lakes  are  not  very  permanent,  but  several  important 
red  lakes  have  come  into  use. 

344.  Eed    Pigments.  —  Various    forms   of   ferric    oxide, 
Fe2O3,  mixed  with  different  proportions  of  silica  or  calcium 
sulphate,  give  the  important  reds  known  as  Venetian  and 
Indian  reds   (Fig.   99,  Frontispiece).     These  shades  re- 
semble the  color  of  red  bricks,  which  have  the  same  color- 
ing matter.     Vermilion  is  a  sulphide  of  mercury  ;  it  is  still 
used  in  artist's  colors,  but  is  being  displaced  in  house  paints 
by  a  lake  known  as  para-nitranaline  red  which  is  fairly 
permanent.     Red  lead,  Pb3O4,  mixed  directly  with  linseed 
oil  without  the  use  of  a  white  pigment,  has  been  until 
recently  the  standard   paint  for   the   protection   of   iron 
work.     It  acts  in  an  unusual  way  with  linseed  oil,  ac- 
quiring a  permanent  "  set "  somewhat  as  plaster  of  Paris 
does  with  water.     Specially  prepared  red  lead  is  used  as 


358  PAINTS,    OILS,   AND   PIGMENTS 

a  substitute  for  vermilion.      Carmine  is  a  red  lake  derived 
from  cochineal. 

345.  Blue  Pigments.  —  The   most   important   blue   pig- 
ment is  ultramarine.     Originally  the  name  was  applied  to 
the  ground  mineral  lapis  lazuli ;  it  was  so  expensive  that 
it  could  be  used  only  in  decorative  work.     In  1828  the 
substance  was  artificially  made  by  fusing  together  alumi- 
num silicate,  sodium  carbonate,  sodium  sulphate,  sulphur, 
and  charcoal.     It  is  of  interest  to  know  that  it  was  prob- 
ably the  first  coloring  matter  produced  synthetically.     It 
is  one  of   the  most  satisfactory  of  all  pigments,  and  is 
wonderfully  permanent  when  used  under  the  proper  con- 
ditions.     Cobalt  blue  gives  a  very  fine  shade  of  color.     It 
was    originally   produced    as    a    combination    of    cobalt 
phosphate  and  aluminum  hydroxide,  but  it  is  now  a  special 
variety  of  ultramarine.     Prussian  blue  has  extraordinary 
coloring  powers.     It  is  produced  by  obtaining  a  precipi- 
tate from  the  action  of  ferrous  sulphate  with  potassium 
ferrocyanide ;    this  precipitate  has  a  bluish  white  color, 
but  when  this  is  treated  with  oxidizing  agents,  the  deep 
blue  pigment  is  obtained.     It  can  also  be  made  directly  by 
the  addition  of  potassium  ferrocyanide  to  a  ferric  chloride 
solution,  but,  this  is  not  cheap  enough  to  be  used  as  a 
commercial  method.     The  permanency  of  Prussian  blue  is 
much   disputed.       When   the   precipitate    is   thoroughly 
washed  to  free  it  from  adhering  salts,  it  is  said  to  be  highly 
permanent. 

346.  Yellow    Pigments.  —  Lead    chr ornate,    known    as 
chrome  yellow,  is  an  intensely  yellow  pigment  that  can  be 
obtained  in  several  different  shades  from  bright  lemon  to 
deep  orange.       It  is  made  by  the  addition  of  potassium 
bichromate  solution  to  lead  nitrate  : 


UNSEED   OIL  359 

2Pb(N03)2  +.K2Cr?07  +  H2O  — *• 

lead  potassium  water 

nitrate  bichromate 

2  PbCr04  +  2  KN03  +  2  HNO3 

lead  potassium  nitric 

chromate  nitrate  acid 

The  varying  shades  are  produced  by  adding  different  acids 
or  alkalies  to  the  solution.  Chrome  yellows  are  very 
permanent.  Yellow  ocher  is  a  beautiful  pigment  that  is 
obtained  from  a  natural  mineral  containing  hydrated  ferric 
oxide  and  clay.  On  being  heated,  this  mineral  turns  to  a 
red  orange  color  known  as  burnt  sienna.  Cadmium  yellows 
are  somewhat  like  chrome  yellow,  but  richer  and  more 
permanent.  Their  use,  on  account  of  their  high  cost,  is 
almost  entirely  restricted  to  artist's  colors.  They  are 
various  forms  of  cadmium  sulphide,  CdS.  Litharge,  lead 
oxide,  PbO,  is  of  a  dull  ocher  color.  It  is  made  by  heat- 
ing lead  in  air  at  a  low  temperature. 

Red,  blue,  and  yellow  are  fundamental  as  pigments, 
since  all  other  colors  can,  theoretically  at  least,  be  ob- 
tained from  them. 

347.  Green  Pigments.  —  Greens  are  usually  mixed  from 
blue  and  yellow  pigments,  such  as  ultramarine  or  Prussian 
blue  and  chrome  yellows.     Paris  green,  used  extensively 
as  an  insect  exterminator,  is  not  much  used  in  paint  because 
it  is  highly  poisonous,  and  fades  rapidly.     It  is  aceto- 
arsenite  of  copper.      Oxide  of  chromium,  emeraude  green, 
gives  a  beautiful    shade  that  is  of   the  highest  order  of 
permanency.     Its  use  is  very  limited  because  of  its  high 
cost. 

VEHICLES 

348.  Linseed  Oil.  —  The  great   bulk  of   all  painting  is 
accomplished  with  the  aid  of  linseed  oil.     This  is  extracted 
by  pressing  the  thoroughly  ground  seed  of  the  flax  plant. 


360  PAINTS,    OILS,  AND  PIGMENTS 

If  heat  is  used  a  larger  yield  of  oil  is  obtained,  but  it  is 
much  darker  in  color.  The  seed  yields  from  25  %  to  32  % 
of  oil.  Like  the  oil  obtained  from  many  other  seeds, 
it  possesses  the  property  of  absorbing  oxygen  from  the 
air,  up  to  as  much  as  18%  of  its  weight,  and  forming 
a  gum-like  substance.  When  spread  as  a  thin  layer  on  a 
surface,  the  oxidation  of  the  oil  produces  a  tough,  im- 
pervious membrane.  Linseed  oil,  therefore,  makes  an 
excellent  holder  for  a  pigment.  The  oil  is  sold  either  raw 
or  boiled.  The  so-called  boiling  is  really  a  heating  of  the 
oil  with  certain  salts  of  lead  or  manganese.  By  this  treat- 
ment the  tendency  of  the  oil  to  acquire  oxygen  is  increased 
and  it  "  dries  "  more  rapidly. 

349.  Other  Vehicle  Oils.  —  Fish  oil  is  obtained  from  men- 
haden fish,  and  dries  as  does  linseed  oil  by  absorption  of 
oxygen.     When  thickened  with  litharge,  it  gives  a  paint 
that  will  stand  high  temperatures.     On  this  account  it  is 
used  in  painting  smokestacks. 

Chinese  wood  oil,  another  drying  oil,  makes  a  paint  that 
will  last  well  in  a  damp  atmosphere.  It  is  much  used  in 
making  enamel  paints.  It  is  also  now  widely  used  in  the 
preparation  of  special  paints.  Poppy  oil  is  an  expensive, 
very  white  oil  that  is  used  in  mixing  artist's  colors. 

350.  Water  Paints  dry  by  evaporation.     The  pigment  is 
held  in  place  by  some  sort  of  cementing  substance  such  as 
glue  or  casein  in  alkaline  solution.     Casein  paints  may  be 
used  for  outside  work  with  a  fair  degree  of  permanency. 
Whitewash  is  slaked  lime  mixed  with  water ;  when  the 
mixture  is  spread  on  a  surface,  the  lime  absorbs  carbon 
dioxide  from  the  air  and  forms  calcium  carbonate.     This 
makes  a  very  cheap  paint  which  does  well  for  inside  work, 
but  will  last  only  a  short  time  when  exposed  to  weather. 

Tempera  Painting  is  sometimes  employed  in  wall  deco- 


COMPOSITION  OF  MIXED  PAINTS  361 

ration.  In  this  process  the  pigment  is  mixed  with  fresh 
plaster  as  it  is  applied.  Some  of  the  world's  most  famous 
paintings,  for  example,  those  in  the  Sistine  Chapel  in  Rome, 
were  executed  in  this  medium. 


READY-MIXED  PAINT 

351.  Holding  Pigments  in  Suspension.  —  When  mixed  with 
linseed  oil  only,  white  lead  does  riot  form  a  permanent 
emulsion.     The  pigment  settles  to  the  bottom  of  the  con- 
tainer, and  forms  a  hard  layer  if  allowed  to  remain  long 
without  stirring.     On  this  account,  "  ready-mixed  paints  " 
were  unknown  until  a  few  years  ago,  and  paint  for  each 
job  was  mixed  fresh  by  the  painter. 

It  was  finally  discovered  that  a  water  solution  of  sodium 
silicate  (water  glass)  would  form  a  permanent  emulsion 
with  white  lead  and  linseed  oil,  and  mixed  paints  based  on 
this  principle  were  put  on  the  market.  This  paint,  how- 
ever, was  not  of  lasting  quality.  Later  many  other 
"  emulsifiers  "  were  found,  but  with  the  increasing  adop- 
tion of  zinc  oxide  and  inert  extenders,  it  has  been  found 
that  a  limited  per  cent  of  water  serves  admirably  the  pur- 
pose of  holding  the  solid  matter  in  suspension. 

352.  Composition  of  Mixed  Paints.  —  The  various  paints 
that  are  on  the  market  vary  widely  in  composition,  and 
there  is,  perhaps,  no  article  that  has  been  so  much  subject 
to  adulteration  and  fraudulent  labeling.     This  undesirable 
condition  exists  because  the  public  is  very  ignorant  of 
what  constitutes  a  good  paint,  and  because  it  takes  time 
for  a  defective  paint  to  reveal  itself.     The  necessity  of 
careful  analysis,  of  weather  tests  where  the  paint  is  ex- 
posed under  known  conditions,  and  of  truthful  labeling 
is  just  being  realized.    Associations  of  paint  manufacturers 


362  PAINTS,    OILS,   AND  PIGMENTS 

have  united  to  conduct  investigations,  and  some  of  the 
states  have  passed  laws  regulating  the  sale  of  paints  and 
have  established  stations  for  testing  purposes. 

A  good  mixed  paint  may -contain  a  considerable  quan- 
tity of  inert  filler,  such  as  silica  or  powdered  marble.  As 
a  base,  it  should  have  a  mixture  of  white  lead  and  zinc 
oxide,  or  one  of  the  lead-zinc  pigments,  or  perhaps  litho- 
phone  for  certain  uses.  As  a  vehicle,  it  should  have  lin- 
seed oil ;  for  special  paints  it  may  have  fish  oil  or  Chinese 
wood  oil.  To  hold  the  solids  in  suspension,  not  more  than 
2  %  of  water  may  be  allowed.  Some  of  the  patent  emul- 
sifiers  do  not  harm  the  paint ;  those  which  are  solutions 
of  rubber  are  considered  allowable ;  others  that  are  essen- 
tially good  oil  varnishes  may  even  improve  the  quality. 
Those  that  are  water  solutions  of  alkaline  salts,  or  those 
that  contain  cheap  varnishes  made  from  rosin  and  lime 
are  harmful.  Good  mixed  paint  should  not  contain  benzine 
or  other  mineral  oil. 

353.  Enamel  Paints  and  Floor  Paints.  —  In  these  paints 
certain  similar  special  characteristics  are  required.     They 
should  dry  rapidly  and  should  give  a  surface  that  is  both 
tough  and  hard,  and  they  should  be  able  to  withstand 
water.     Lithophone  is  said  to  make  an  ideal   pigment, 
and  Chinese  wood  oil  a  good  vehicle.     Good  resin-oil  var- 
nish is  added  to  insure  rapid  drying  and  a  tough  surface. 
A  considerable  quantity  of  inert  filler  is  also '  frequently 
used. 

354.  Stains.  —  The  purpose  of  a  stain  is  primarily  to 
color  a  surface,  and  hence  covering  power  is  not  desired. 
Consequently,  little  or  no  white  pigment  is  used,  and  the 
color  is  sometimes  furnished  by  a  dye  instead  of  a  pig- 
ment.    A  small  quantity  of  starch  or  silica  is  sometimes 
used  to  give  a  slight  body  to  the  stain.      Water  stains  and 


QUALITY  IN   VARNISHES  363 

some  of  the  newer  stains  that  are  made  with  benzine, 
wood  alcohol,  or  acetone  are  merely  dyes,  and  do  not  in 
any  sense  form  a  protective  coating.  Oil  stains  use  tur- 
pentine and  linseed  oil,  and  are  used  where  a  "  mat "  or 
soft  finish  is  desired.  Varnish  stains  dry  very  quickly 
and  give  a  polished,  shiny  surface.  As  the  name  implies, 
the  vehicle  is  mainly  varnish. 

355.  Japan  and  Driers.  —  Raw  linseed  oil  absorbs  oxy- 
gen from  the  air  very  slowly,  and  a  paint  made  with  its 
aid,  if  allowed  to  harden  naturally,  .would  gather  a  large 
amount  of  dirt  and  dust.     To  hasten  the  process  driers 
are  added  to  the  oil.     Japan  driers  are  made  by  fusing 
resins  with  metallic  bases  and  diluting  the  product  with 
benzine  or  turpentine  or  a  mixture  of  both.     Oil  driers 
are  made  by  heating  linseed  oil  with  lead  or  manganese 
compounds  until  a  thick  product  is  obtained,  and  diluting 
the  product  with  benzine  or  turpentine. 

Driers  are  good  examples  of  catalytic  agents.  A  small 
amount  of  drier  will  hasten  the  hardening  of  a  very  large 
amount  of  oil ;  from  J  to  1  %  of  the  weight  of  the  oil  is 
usually  sufficient. 

VARNISHES 

356.  Quality  in  Varnishes.  —  A  varnish  is  a  finishing  or 
protective  coat  that  is  transparent  and  reveals  the  grain 
of  the  wood.     As  with  mixed  paints,  there  is  a  great  vari- 
ation in  the  quality  of  varnishes  as  found  on  the  market. 
A  good  varnish  should  stand  water,  and  should  not  "  dust  " 
when  scratched.     The  water  test  is  very  easily  made  by 
allowing  a  wet  sponge  to  stand  on  the  surface  over  night. 
If  the  quality  is  good,  either  no  spot  at  all,  or  one  that 
disappears  very  quickly,  will  form  where  the  water  touched 
the  varnish.     The   "dusting"  is  tested  by  pushing  the 


364  PAINTS,    OILS,   AND  PIGMENTS 

point  of  a  knife  across  the  surface.  A  poor  varnish  will 
break  into  a  powder  which  will  fly  from  the  point,  while 
a  good  article  will  yield  a  fine  ribbon  as  the  knife  point 
plows  into  the  surface. 

357.  Classification    of   Varnishes.  —  Varnishes    may    be 
grouped  into  three  classes.     Spirit  varnishes  are  made  by 
dissolving  gums  or  resins   in  volatile   solvents   such   as 
wood,  or  grain  alcohol.     These  dry  by  simple  evapora- 
tion of  the  solvent,  and  the  gum  is  left  unchanged  except 
that  it  has  been  spread  out  in  a  thin  film.     To  this  class 
belong  the  varnishes  known  as  shellac,  mastic,  sandarac, 
and  dammar.      Turpentine  varnishes  are  made  by  dissolv- 
ing gums  in  hot  turpentine.    As  these  dry,  the  oil  becomes 
resinous,  and  the  resulting  film  is  tougher,  as  a  rule,  than 
that  obtained  from  spirit  varnishes.     The  most  important 
are  the  oil  varnishes,  made  by  dissolving  a  melted  gum  in 
hot  linseed  oil.     These  afford  very  tough,  water- resisting 
films.     The  gums  used  are  copal,  anime,   dammar,   and 
amber. 

358.  Adulteration  in  Varnishes.  —  Ordinary  rosin  is  ob- 
tained in  large  quantities  in  the   making  of  turpentine 
from  coniferous  trees.     It  is  largely  used  as  an  adulterant 
of  expensive  gums  used  in  varnish  making,  and  also  as 
the  foundation  of  a  very  inferior  varnish  much  used  on 
cheap  furniture.     The  rosin  is  fused  with  quicklime  and 
the  product  used  as  a  gum.     It  gives  a  brilliant,  but  very 
brittle,  varnish. 

SUMMARY 

Paints  are  mixtures  of  pigments  and  vehicles. 

A  Good  White  Pigment  must  have  high  covering  power,  must 
mix  well  with  the  vehicle,  forming  a  combination  that  will  spread 
well  with  the  brush,  and  must  resist  the  action  of  weather  and 


SUMMARY  365 

light.  Important  white  pigments  are  :  white  lead,  zinc  oxide, 
sublimed  white  lead  (a  mixture  of  lead  sulphate  and  zinc),  and 
lithophone. 

Extenders  or  Inert  Pigments  are  much  used  to  improve  the 
wearing  qualities  of  paint,  although  they  diminish  the  covering 
power  and  the  ease  of  its  application.  Important  diluents  of  this 
sort  are  :  finely  ground  barium  sulphate,  marble,  chalk,  silica,  and 
China  clay. 

Colored  Pigments  should  have  permanency  and  high  coloring 
power.  They  are  frequently  oxides  or  sulphides  of  metals. 
Among  important  pigments  are  the  ochres  and  siennas,  derived 
from  natural  minerals  containing  ferric  oxide  and  clay,  red  lead, 
litharge,  vermilion,  various  lakes,  ultramarine  blue,  cobalt  blue, 
Prussian  blue,  chrome  yellows  (lead  chromates),  cadmium  sul- 
phide, oxide  of  chromium. 

Linseed  Oil  is  the  most  important  vehicle.  It  hardens  by  ab- 
sorption of  oxygen.  Boiled  linseed  oil  is  oil  that  has  been  heated 
with  lead  or  manganese  compounds ;  it  "  dries  "  more  rapidly 
than  the  raw  oil.  Fish  oil,  Chinese  wood  oil,  and  poppy  oil  also 
harden  by  absorption  of  oxygen. 

Water  with  glue,  casein,  or  linseed  oil  soap  serves  as  a  vehicle 
in  so-called  water  paints. 

In  Ready-mixed  Paints  the  principal  difficulty  to  overcome  is 
the  tendency  of  pigments  to  settle  as  the  can  of  paint  stands. 
To  counteract  this,  ah  emulsifier  is  used.  Two  per  cent  of  water 
will  answer  the  purpose,  and  other  devices  are  used. 

Stains  differ  from  paints  in  having  very  slight  covering  power. 

Japan  and  other  Driers  are  compounds  formed  by  heating  lin- 
seed oil  with  lead  or  manganese  compounds.  They  act  catalyti- 
cally  to  hasten  the  absorption  of  oxygen  by  the  paint. 

Varnishes  differ  from  paint  in  having  a  transparent  gum  instead 
of  pigment  to  give  body  to  the  protecting  coating. 

Good  varnishes  do  not  turn  white  in  contact  with  water,  and 
on  drying  leave  a  tough  rather  than  a  brittle  coating.  Spirit 


366  PAINTS,   OILS,   AND  PIGMENTS 

varnishes  dry  by  evaporation  of  the  volatile  solvent  in  which  the  gum 
is  dissolved.  Turpentine  and  oil  varnishes  dry  by  absorption  of 
oxygen,  and  are  best  for  most  purposes.  Oil  varnishes  are 
made  by  dissolving  melted  gums,  such  as  copal  and  dammar, 
in  hot  linseed  oil. 

The  Chief  Adulteration  of  Varnishes  is  in  the  use  of  ordinary 
rosin  in  place  of  better  gums.  It  makes  a  brittle  varnish  that 
readily  turns  white  with  water. 


EXERCISES 

1.  Why  is  white  lead  such  a  good  paint  base  ? 

2.  How  is  white  lead  made  ?     How  is  zinc  oxide  made  ? 

3.  What  is  lithophone  ?     How  is  it  made  ?     What  is  sub- 
limed white  lead  ? 

4.  Would  ground  marble,  or  silica,  alone  make  a  good  paint 
base  ?     Why  ?     What  advantages  has  it  as  a  filler  ? 

5.  What  is  the  composition  of  white  lead  ?     Which  con- 
stituent gives  the  desirable  characteristic  of  making  it  mix  well 
with  linseed  oil  ? 

6.  What  disadvantage  is  there  in  the  use  of  zinc  oxide  as  a 
paint  base  ? 

7.  Lead  sulphide  is  a  black  substance.     Why  do  artists  in 
making  mural  decorations  for  cities  where  much  coal  is  burned 
prefer  zinc  oxide  or  a  mixture  of  zinc  oxide  and  lead  sulphate 
as  their  paint  base  ? 

8.  Name  five  very  permanent  colored  pigments. 

9.  Why  is  a  considerable  amount  of  white  pigment  used  in 
all  paints  ? 

10.  Which  is  more  important  in  a  colored  pigment,  covering 
power  or  tinctorial  power  ? 

11.  Why  are  dyes  not  used  more  frequently  to  furnish  the 
coloring  matter  of  paints  ? 


EXERCISES  367 

12.  In  making  paints  why  is  it  important  to  have  pigments 
ground  extremely  fine  ? 

13.  What  is  meant  by  the  term  "  drying  oil "  ?     Name  four 
drying  oils.     Does  oil  paint  lose  or  gain  in  weight  in  drying  ? 
Why  ?     Water  paint  ? 

14.  Why  is  linseed  oil  so  commonly  used  as  a  paint  vehicle? 
How  is  it  made  ?     What  is  the  difference  between  raw  and 
boiled  oil  ? 

15.  What  particular  advantage  has  fish  oil  ?     Chinese  wood 
oil? 

16.  Of  what  advantage  is  it  to  the  consumer  to  be  able  to 
buy  ready-mixed  paint  ? 

17.  What  was  the  chief  difiiculty  to  be  overcome  in  making 
ready-mixed  paint  ? 

18.  What  qualities  would  be  given  to  a  paint  by  the  addition 
of  varnish  ?     For  what  purposes  would  such  a  paint  be  desir- 
able? 

19.  What  are  the  tests  for  a  good  varnish  ? 


CHAPTER   XXXII 


DISTILLATION  OF  PETROLEUM,  WOOD,  AND 

COAL 

359.   Crude   Petroleum.  —  Petroleum    is   an   oily    liquid 
found  in  the  earth.     It  varies  in  color  from  light  yellow 

to  black  and  ranges  from  a  thin 
to  a  very  thick,  sticky  liquid. 
The  most  commonly  accepted 
theory  of  its  origin  is  that  it 
was  formed  by  the  decomposi- 
tion of  animal  or  vegetable 
matter  or  both.  This  country 
is  the  largest  oil  producer. 
Among  its  well-known  oil  fields 
are  those  of  Oklahoma,  Cali- 
fornia, Illinois,  Texas,  and 
Pennsylvania  with  states  ad- 
joining it.  The  largest  foreign 
fields  are  those  of  Russia, 
Galicia,  Rumania,  and  the  East 
Indies. 

Petroleum  occurs  in  oil-bear- 
ing sandstones  and  conglom- 
erates, called  "  oil  sands.'7  It 
is  obtained  by  drilling  wells 
through  the  overlying  strata, 
sometimes  to  a  depth  of  3000 

FIG.  IOO.-SPOUTING  OIL  WELL.     feet'      The    rock   at  the   bottom 

of  the  well  is  often  shattered 

by  the  explosion  of  several  gallons  of  nitroglycerin ;  this 
is  called  "shooting  the  well."     Only  a  small  portion  of 


CRUDE    OIL    STILLS  369 

the  petroleum  is  now  refined  in  the  oil  fields,  the  greater 
part  being  transported  and  refined  at  the  seaboard.  In 
one  pipeline  in  this  country,  oil  is  pumped  from  Oklahoma 
to  the  Atlantic  coast,  a  distance  of  1600  miles. 

REFINING  OF  PETROLEUM 

360.  Object.  —  As  petroleum  is  a  complex  mixture   of 
the  paraffin  hydrocarbons  having  different  boiling  points, 
the  refining  process  is  chiefly  one  of  fractional  distillation. 
After  the  distillation  follows  the  removal  of  impurities  that 
would  interfere  with  the  use  of  the  oils.     The  fractional 
distillation  is  conducted  according  to  the  nature  of  the  oil 
and  according  to  the  nature  of  the  products  desired. 

361.  Crude  Oil  StiUs.  — The  crude  oil  is  heated  in  stills, 
which  are  steel  boilers,  set  in  brickwork,  each  with  a  capac- 
ity of  1000  to  1200  barrels.     The  stills,  which  are  often  ar- 
ranged in  pairs,  are  heated  by  furnaces  extending  the  entire 
length  of  one  side  of  each  still.     The  fuel  is  either  oil,  coke, 
or  coal,  depending  upon  the  relative  cheapness  at  the  re- 
finery.    A  series  of  condensers  provide  for  the  conden- 
sation of  vapors  according  to  their  boiling  points.     An 
arrangement  of  pipes  is  used  to  run  the  fractional  distil- 
lates into  tanks  in  accordance  with  their  specific  gravities. 
Coke  is  left  as  a  residue  in  the  still,  and  has  to  be  removed 
before  another  charge  of  oil  is  run  in. 

A  good  idea  of  the  refining  process  may  be  obtained 
from  the  diagram  (Fig.  101).  A  mixture  of  vapors  passes 
out  from  the  top  of  the  still  through  a  large  iron  pipe  to 
the  bottom  of  the  condenser  B.  The  lower  half  of  this  is 
a  brick  tower  filled  with  cobblestones  resting  on  a  grating. 
Above  the  cobblestones  are  more  than  50  vertical  pipes 
held  in  place  by  a  perforated  iron  plate  at  the  top  of  the 
tower.  Condenser  O  is  similar  in  construction  to  con- 


370 


PETROLEUM,    WOOD,   AND   COAL 


denser  B.  The  bottom  discharge  pipe  from  B  is  a  long 
coil.  The  bottom  discharge  pipe  from  C  and  the  pipe 
coming  out  from  the  top  of  Q  are  each  connected  with  a 
large  coil  of  pipe  in  the  tank  .Z),  through  which  water  circu- 
lates. Each  of  these  condensing  coils  delivers  a  stream  of 


FIG.  101.  —  FRACTIONAL  DISTILLATION  OF  CRUDE  PETROLEUM. 

oil  to  the  "  running  house,"  where  the  "still-man  "  watches 
the  streams  of  oil  and  from  time  to  time  takes  their  specific 
gravity.  Movable  boxes,  with  a  pipe  connection  beneath, 
seen  at  _#,  permit  him  to  direct  the  stream  from  any  one  of 
the  spouts  into  the  tank  which  temporarily  stores  the  oil 
of  a  specific  gravity  between  certain  limits. 

In  describing  the  distillates,  it  is  convenient  to  use  the 
term  heavy,  meaning  oils  of  high  boiling  points,  which  are 
easily  condensed.  Light  means  oils  of  low  boiling  points. 
In  the  early  part  of  the  distillation  the  heavy  oils  are  con- 
densed in  the  cobblestone  part  of  the  tower  and  run  back 
to  the  stills  through  a  small  pipe.  Vapors  that  pass 


STEAM   STILLS  371 

through  the  cylindrical  tower,  but  which  are  too  heavy  to 
rise  through  ^the  rectangular  tower,  flow  out  at  the  bottom 
of  the  tower  through  a  cooling  coil  in  the  tank  and  are 
conducted  to  the  running  house.  This  stream  is  known  as 
the  intermediate  or  gas  oil.  When  the  intermediate  dis- 
tillate shows  a  specific  gravity  of  0.85  in  the  running  house, 
the  run-back  to  the  still  is  closed.  The  distillate  from 
the  bottom  of  the  cobblestone  tower  then  runs  down 
through  a  coil  in  the  tank  and  is  known  as  the  paraffin 
qil  distillate.  The  light  vapors,  which  pass  through  both 
towers,  pass  downward  from  the  top  of  tower  O  through 
a  pipe  to  a  cooling  coil,  which  discharges  in  the  running 
house.  This  stream,  which  is  termed  crude  naphtha,  con- 
tains gasoline,  benzine,  and  kerosene,  the  light  oils.  Thus 
at  this  stage  of  the  process  the  three  streams  in  the  running 
house  are  the  paraffin  oil  distillate,  the  intermediate  oil, 
and  the  crude  naphtha  or  light  oil. 

362.  Steam  Stills.  — The  intermediate  oil  and  the  light 
oil  are  again  fractionally  distilled  in  steam  stills  and  the 
distillates  separated  according  to  their  specific  gravities. 
The  oil  to  be  distilled  is  pumped  from  the  running  house 
to  another  cylindrical  still  heated  by  either  live  or  exhaust 
steam.  A  continuous  stream  of  oil  flows  into  the  steam 
still  at  the  bottom,  and  a  continuous  stream  of  vaporized 
oil  passes  out  at  the  top.  Fractional  distillates  of  a.  simi- 
lar range  of  specific  gravities  are  sometimes  combined 
and  again  steam -^stilled.  The  object  of  these  repeated 
distillations  is  to  get  definite  grades  of  oil  of  certain 
specific  qualities. 

Thus  the  crude  naphtha,  which  is  the  light  oil  distillate 
having  specific  gravity  of  0.73  or  less,  yields  a  number  of 
fractions.  The  more  important  of  these  in  the  order  of 
the  increasing  specific  gravity,  are  -petroleum  ether, 


372  PETROLEUM,    WOOD,   AND   COAL 

naphtha,  and  benzine.  All  these  are  trade  names  given  to 
mixtures  of  varying  composition.  In  some  cases  the  trade 
name  may  cover  several  grades,  each  of  which  is  sold 
according  to  a  definite  specific  gravity  and  an  approximate 
boiling  point.  Thus  there  are  several  benzines  and  several 
naphthas  on  the  market. 

From  the  distillates  with  a  specific  gravity  above  0.73, 
but  below  0.83,  coming  from  either  the  crude  oil  still  or  the 
steam  still,  there  are  obtained  the  burning  oils  or  kerosenes. 
These  oils  are  distilled  to  a  definite  specific  gravity  and 
fire  test,  the  temperature  at  which  the  oil  gives  off  enough 
vapor  to  maintain  a  continuous  flame  if  ignited.  Thus  the 
best  grade  of  kerosene  sold  in  this  country,  water  white, 
has  a  fire  test  of  150°  F.  (65.5°  C.).  Common  refined  oil, 
known  as  export  oil,  has  a  fire  test  of  110°  F.  (43.3°  C.). 
*The  burning  oil  distillates  which  do  not  have  a  good  color 
are  run  into  the  gas  oil  distillate,  which  is  used  for  car- 
bureting water  gas  (§371). 

363.  Removal  of  Impurities. — All  the  burning  oils  when 
they  come  from  the  still  contain  impurities  which  interfere 
with  their  burning  qualities.  These  foreign  substances 
are  removed  in  the  agitators.  The  oil  is  first  treated  with 
concentrated  sulphuric  acid,  then  washed  with  water.  It 
is  next  treated  with  sodium  hydroxide  or  carbonate  to 
neutralize  the  acid,  and  again  washed  with  water.  During 
each  of  these  operations,  the  mixture  is  stirred  violently 
by  a  powerful  air  blast.  The  oil  is  finally  treated  with 
fuller's  earth  to  clarify  or  brighten  it.  From  the  agitators 
the  oil  is  run  into  settling  tanks,  in  order  to  remove  the 
water  and  the  fuller's  earth,  and  then  goes  to  the  storage 
tanks. 

Canadian  petroleums  and  some  of  those  from  the  Middle 
West  contain  sulphur  compounds,  which  give  an  offensive 


GASOLINE  373 

odor  in  burning.  As  these  compounds  are  not  removed 
by  the  usual  processes  of  refining,  special  means  have 
been  devised  for  their  elimination,  viz.,  distillation  in  the 
presence  of  copper  oxide.  By  this  distillation,  carbon 
disulphide,  methyl  sulphide,  and  other  sulphur  compounds 
are  removed. 

364.  Paraffin  Oil  Distillate. — This  is  subjected  to  redis- 
tillation, and  other  processes  are  also  employed,  such  as 
chilling  and  squeezing  in  filter  presses  to  separate  waxes, 
sweating  with  steam,  and  treatment  with  sulphuric  acid. 
A  wide  range  of  products  is  obtained — lubricating  oils  of 
low  or  medium  viscosity,  heavy  lubricating  oils,  vaseline 
or  petrolatum,  soft  waxes,  and  hard  waxes,  such  as  the 
refined  paraffin  of  commerce. 

Coke  is  the  residue  left  in  the  crude  oil  still  and  has  to 
be  cleaned  out  with  sharp-pointed  shovels.  This  coke  is 
used  in  making  the  carbons  for  arc  lamps,  but  owing  to 
the  oversupply  for  that  purpose  much  of  it  is  used  as  a 
fuel  to  heat  the  crude  oil  stills. 

365.  Gasoline.  — When  the  supply  of  gasoline  was  plen- 
tiful enough  to  meet  the  demand,  it  contained  the  hydro- 
carbons found    in   refined   naphtha,  benzine,  and  ligroin. 
As  stated  in  §  361,  the  vapors  of  the  heavy  oils  are  con- 
densed in  the  early  part  of  the  distillation  and  run  back 
into  the  still.     There  they  strike  the  boiling  oil  which  is 
raised   to  a   higher    temperature  and  are  converted  into 
hydrocarbons  of  a   lower  molecular    weight  and    boiling 
point.     This  process    is.  called  cracking  and    results    not 
only  in  the  formation  of  lower  hydrocarbons  of  the  par- 
affin series,  but  ethylene  hydrocarbons  as  well. 

The  hope  of  meeting  the  ever  increasing  demand  for 
gasoline  seems  to  depend  upon  processes  of  converting 
the  heavier  oil  distillates  into  the  lighter  oils.  Several 


374  PETROLEUM,    WOOD,  AND   COAL 

such  processes  are  in  the  last  stages  of  experimental 
development,  with  very  favorable  outlook.  Until  these 
hopes  are  realized,  users  of  gasoline  will  have  to  be  con- 
tent with  a  poor  quality,  as  some  of  the  oils  of  higher  boil- 
ing points  have  to  be  mixed  with  the  true  gasoline  fractions 
to  supply  the  commercial  demand  for  the  liquid. 

366.  Destructive  Distillation.  —  The  distillation  of  petro- 
leum which  has  just  been  described  is  essentially  the  same 
as  the    distillation  of   a   mixture    of   water   and   alcohol 
described  in  Chapter  XVI.     In  this  way  a  partial  separa- 
tion of  the  liquids  is  accomplished,  for  the  first  portion  of 
the  distillate  contains  a  larger  percentage  of  the  liquid 
having  the  lower  'boiling  point.      When   solids,  such  as 
wood  and  coal,  are  heated  out  of  contact  with  the  air,  not 
only  are  the  liquids  present  distilled  off  as  such,  but,  as 
the  temperature  increases,  some  of  these  liquids  and  some 
of  the  solid  compounds  present  are  cracked  (§  365).     As 
a  result,  vapors  of  substances  that  were  not  present  in 
the  original  material  pass  off   and  are  condensed.     The 
process  of  breaking  up  a  complex  substance  into  a  number 
of  simpler  substances  by  heating  out  of  contact  with  air 
and  condensing  the  resulting  vapors,  is  called  destructive 
distillation. 

367.  Destructive  Distillation  of  Wood.  —  The   destructive 
distillation  of  wood  was  first  carried  on  simply  to  obtain 
charcoal.     Wood  was  piled  loosely  and   the   whole   pile 
covered  with  turf.     The  wood  was  set  on  fire  and  a  por- 
tion of  it  allowed  to  burn  in  a  limited  supply  of  air  enter- 
ing  through   air   holes    in   the   turf.     The   heat   of   the 
burning  wood  was  enough  to  drive  off  the  volatile  matter 
from  the  remainder  of  the  wood.     The  volatile  products 
were  allowed   to  escape.     To-day  we  realize  that  these 
volatile  products  are  more  valuable  than  the   charcoal. 


DESTRUCTIVE  DISTILLATION  OF   WOOD        375 

Until  wood  became  too  valuable,  it  was  used  in  making 
illuminating  gas. 

In  a  modern  plant,  the  destructive  distillation  of  wood 
is  carried  on  in  retorts  or  in  rectangular  ovens.  The 
charge  varies  from  one  half  a  cord  to  five  cords  of  wood,  in 
the  form  of  cord  wood  or  billets  or  chips.  The  charcoal 
remains  in  the  oven  or  retorts,  while  the  volatile  products 
pass  into  a  vertical,  tubular  condenser  kept  cool  by  water 
circulating  in  an  outer  shell.  The  materials  recovered 
consist  of  gases,  which  are  used  as  fuels  ;  a  water  solution, 
known  as  pyroligneous  acid  ;  and  tarry  substances. 

The  condenser  liquor  from  the  distillation  is  usually  in 
three  layers  :  an  upper  layer  of  tarry  oils,  an  intermediate 
layer  of  pyroligneous  acid,  and  a  lower  layer  of  tar.  The 
pyroligneous  acid  contains  acetic  acid,  wood  alcohol, 
acetone,  and  certain  other  compounds. 

The  pyroligneous  acid  is  usually  distilled ;  the  volatile 
wood  alcohol  passes  off  first  and  is  later  purified.  The 
acetic  acid  follows.  The  latter  is  called  distilled  "  wood 
vinegar."  It  is  neutralized  with  lime  forming  gray  ace- 
tate of  lime,  or  with  sodium  carbonate.  Acetic  acid  is 
obtained  from  calcium  acetate  or  from  sodium  acetate 
by  distilling  an  excess  of  either  of  these  salts  with  con- 
centrated hydrochloric  acid.  The  distillate  is  redistilled 
over  calcium  acetate  to  remove  any  hydrochloric  acid 
that  came  over  with  the  acetate  acid.  Glacial  acetic 
acid  is  made  by  distilling  pure  anhydrous  sodium  acetate 
with  concentrated  sulphuric  acid. 

Acetone,  CH3 .  CO  .  CH3,  distills  over  with  the  wood 
alcohol  and  is  separated  from  it  with  difficulty.  Com- 
mercially acetone,  is  majie  by  the  dry  distillation  of  the 
gray  acetate  of  lime. 

In  the  distillation  of  hard  wood,  charcoal,  alcohol,  and 
acetates  are  the  main  products. 


376  PETROLEUM,    WOOD,   AND    COAL 

Resinous  ivoods  yield  tar,  turpentine,  and  charcoal. 
The  distillation  of  wood  has  become  a  very  important 
and  highly  specialized  industry. 

368.  Destructive  Distillation  of  Coal.  —  The  manufacture 
of  illuminating  gas  from  coal  is  a  process  of  destructive 
distillation.  The  bituminous  coal  used  contains  from 
30  %  to  40  %  of  volatile  matter  and  is  heated  in  iron 
retorts.  The  heat  must  be  sufficient  to  carbonize  the  coal 
and  be  maintained  long  enough  to  complete  the  decomposi- 
tion and  the  distillation. 

The  first  step  in  the  carbonization  begins  at  400°  C.  and 
is  probably  a  fusion,  as  the  temperature  remains  constant 
for  some  time.  As  the  heat  increases,  the  carbon  com- 
pounds produced  in  the  first  stage  split  into  simpler  com- 
pounds. Some  of  these,  striking  the  very  hot  sides  of  the 
retort,  undergo  further  reactions  resulting  in  the  forma- 
tion of  complex  compounds.  The  temperature  and  time 
taken  for  the  distillation  determine  in  great  measure  the 
relative  amounts  of  the  various  gaseous  products.  It  has 
been  found  desirable  to  have  the  pressure  in  the  retorts 
approximate  that  of  the  outside  air.  A  pump  known  as 
the  exhauster  brings  this  about. 

In  a  modern  gas  plant,  ingenious  mechanical  devices 
are  used  for  charging,  opening,  and  emptying  these 
retorts  (§  370,  Fig.  102).  The  quality  of  the  coke  ob- 
tained depends  upon  the  time  and  temperature  of  the 
destructive  distillation.  A  low  temperature  and  a  short 
time  give  a  soft  porous  coke  containing  12  %  of  volatile 
matter.  As  the  temperature  increases  and  the  time 
lengthens,  a  harder,  denser  coke  of  a  metallic  appearance, 
suitable  for  foundry  purposes,  is  obtained. 

The  products  that  pass  out  of  the  retorts  are  illumi- 
nating gas  with  various  gaseous  impurities,  an  ammoniacal 


THE  MANUFACTURE   OF  ILLUMINATING   GAS     377 

liquid,  and  coal  tar  vapor  or  fog.  The  non-condensible 
gaseous  impurities  are  chiefly  ammonia,  NH3,  cyanogen, 
C2N2,  hydrogen  sulphide,  H2S,  and  carbon  dioxide,  CO2. 
The  coal  tar  contains  a  number  of  organic  (carbon)  com- 
pounds. The  valuable  by-products  of  the  process,  then, 
are  coke,  ammonia,  and  coal  tar  products.  It  has  -been 
estimated  that  a  ton  of  gas  coal  of  average  quality  yields 
about  two  thirds  of  a  ton  of  coke,  13  gallons  of  tar, 
20  pounds  of  ammonium  sulphate  (from  the  neutralization 
of  the  ammonia  water),  and  12,000  cubic  feet  of  gas. 
The  coal  tar  is  collected  from  the  various  gas  plants  and 
a  number  of  valuable  carbon  compounds  are  extracted  from 
it  in  an  establishment  devoted  to  that  purpose.  Among 
these  compounds  may  be  mentioned  naphtha,  benzene, 
toluene,  heavy  oils,  carbolic  acid  and  its  derivatives,  and 
naphthalene,  familiar  in  its  crude  form  as  moth  balls. 

In  a  gas  plant,  there  are  three  main  steps  in  the  separa- 
tion of  the  products  leaving  the  retorts,  the  removal  of  the 
coal  tar,  the  removal  of  the  ammonia,  and  the  purification 
of  the  illuminating  gas  from  gaseous  impurities.  The 
action  in  each  part  of  the  apparatus  is  briefly  stated  in 
the  following  section. 

369.   Steps  in  the  Manufacture  of  Illuminating  Gas.  — 

Retorts.  A  carbonization  of  soft  coal,  leaving  coke  in 
retort ;  gases  and  tarry  smoke  pass  to  hydraulic  main. 

Hydraulic  main.  Part  of  tar  condensed  and  deposited  ; 
some  ammonia  dissolved. 

Primary  condenser.  Gas  and  tarry  vapor  cooled  ;  some 
tar  deposited. 

Tar  extractor.     Tar  is  removed. 

Exhauster.  Proper  pressure  maintained  in  retorts ; 
gas  forced  through  train  of  scrubbers  and  purifiers. 


378  PETROLEUM,    WOOD,  AND   COAL 

Naphthalene  scrubber.  Naphthalene  absorbed  by  some 
heavy  tar  oil. 

Cyanogen  scrubber.  Cyanogen  absorbed  by  alkaline 
solution  of  ferrous  sulphate. 

Secondary  condenser.  Gases  cooled  so  that  the  remain- 
ing ammonia  may  be  absorbed  by  water  in  the  ammonia 
washer. 

Ammonia  washer.     Remaining  ammonia  absorbed. 

Purifiers.  Hydrogen  sulphide  absorbed  by  ferric  oxide. 
(Sometimes  additional  purifier  for  removal  of  organic 
sulphur  compounds.) 

Holder.     Gas  ready  for  distribution. 

370.  Continuous  Process.  — In  Fig.  102  is  shown  a  sec- 
tional view  of  a  gas  retort,  in  which  the  process  goes  on 
without  interruption  for  removing  coke  from  the  retorts 
and  inserting  a  fresh  charge  of  coal.  The  retorts,  a  sec- 
tion of  one  of  which  is  shown,  are  vertical  and  increase  in 
diameter  from  top  to  bottom.  The  coal  is  admitted 
through  the  coal  gate  at  intervals  from  the  storage  bin  on 
the  top  floor  to  the  charging  hopper  immediately  below. 
From  this  hopper  it  falls  continuously  into  the  retort  be- 
low, as  needed.  This  retort  is  heated  by  the  combustion 
of  producer  gas  from  the  gas  producer  on  the  furnace 
floor.  The  hot  gases  from  the  producer  first  strike  the 
retorts  near  the  top  and  then  are  forced  to  pass  around 
and  downward  between  the  retorts,  as  shown  by  the 
arrows.  After  parting  with  most  of  their  heat,  these 
gases  finally  escape  into  the  chimney. 

The  gas  coal  in  the  retort  begins  to  distil  at  the  top 
where  the  heat  first  strikes  it.  As  the  coal  works  down 
in  the  retort  the  proportion  of  coal  decreases  and  that  of 
coke  increases,  as  shown  in  the  illustration.  The  illumi- 
nating gas  works  its  way  upward  to  the  pipes  marked 


CONTINUOUS  PROCESS 


379 


FIG.   102.  —  VERTICAL  RETORTS  OF  THE  CONTINUOUS  PROCESS  FOR  MAKING 
ILLUMINATING  GAS. 


380 


PETROLEUM,    WOOD,   AND   COAL 


"  Gas "  and  through  them  to  the  hydraulic  main  on  the 
pipe  gallery.  It  is  then  purified  as  outlined  in  §  369. 
The  compact  mass  of  coke  at  the  bottom  is  broken  up  by 
the  extractors  shown  at  the  bottom  and  falls  into  dis- 
charging hoppers,  from  which  it  is  periodically  removed. 
Vertical  retorts  operated  in  this  way  yield  more  gas  per 
pound  of  coal  and  gas  of  higher  illuminating  power  than 

horizontal  or  inclined  retorts, 
in  addition  to  avoiding  the 
labor  and  loss  of  time  involved 
in  cleaning  and  discharging 
horizontal,  intermittently  oper- 
ating retorts. 

371.  Commercial  Manufacture 
of  Water  Gas.  —  The  essential 
steps  in  the  manufacture  of 
water  gas  for  illuminating  pur- 
poses and  for  producer  gas 
have  been  already  described  in 
§§  96,  97.  For  purposes  of 
comparison  with  illuminating 
gas  and  because  the  two  il- 
luminants  are  often  made  in 
the  same  plant,  a  few  details 
of  a  modern  water  gas  gener- 
ator are  given  here.  The  gen- 
erator shown  in  Fig.  103  has 
FIG.  103.— WATER  GAS  GENER-  the  carburetor  and  super- 
ATOR.  heater  placed  directly  above 

the  fire  chamber,  and  perma- 
nently connected  with  each  other  by  an  opening  at 
their  lower  ends.  Valves  are  located  in  the  connect- 
ing gas  passages  at  the  points  marked  V.  The  caps 


COMMERCIAL  MANUFACTURE   OF   WATER   GAS     381 

0  and  C'  are  valves  opening  into  stacks  leading  to 
the  air. 

In  starting  the  operation  of  the  generator,  a  blast  of  air 
is  blown  up  through  the  hard  coal  or  coke  from  below, 
the  cap  valve  C  and  the  other  valves  between  it  and  the 
fire  chamber  being  open.  In  this  way  the  coal  is  soon 
brought  to  incandescence.  The  cap  0  is  then-closed  and 
the  valve  leading  into  the  upper  end  of  the  carburetor 
is  opened.  This  permits  the  heated  gases  to  pass  down 
through  the  carburetor,  which  is  a  chamber  filled  with  a 
checkerwork  of  brick,  and  up  through  the  superheater,  a 
similar  chamber,  then  out  through  G',  which  is  opened  for 
the  purpose,  into  a  stack.  This  is  called  the  "blow"  and 
is  continued  until  the  carburetor  and  superheater  have 
reached  the  proper  working  temperature. 

The  air  blast  is  then  shut  off  and  steam  is  admitted 
through  one  of  the  steam  pipes  and,  at  the  same  time,  gas 
oil  is  sprayed  into  the  carburetor  through  the  oil  pipe. 
The  steam  in  passing  through  the  incandescent  coal  re- 
acts with  it,  with  the  formation  of  carbon  monoxide  and 
hydrogen. 

C  +  H20   — >-   CO       +       H2 

carbon      steam      carbon  monoxide      hydrogen 

This  mixture  is  enriched,  that  is,  given  added  illuminating 
power,  by  taking  up  gases  produced  by  the  cracking  of 
oil  in  the  carburetor;  the  cracking  process  is  continued 
and  the  mixture  is  made  uniform  by  passing  through  the 
superheater.  The  cap  valve  0'  is  closed  and  the  enriched 
gas  passes  out  through  the  pipe  toward  the  left  at  the  top 
of  the  superheater. 

The  carburetor  in  a  water  gas  plant  is  likely  to  become 
overheated,  as  the  gas  passes  directly  from  the  fire  chamber 
into   it.     By   proper   manipulation   of   the  valves  of  the 
' 


382  PETROLEUM,    WOOD,   AND   COAL 

generator  shown  in  the  illustration,  when  the  carburetor 
is  sufficiently  heated,  the  gas  may  be  "by-passed,"  that 
is,  the  gas  from  the  fire  chamber  may  be  passed  below  the 
carburetor  directly  across  to  the  superheater.  The  oil 
gas  from  the  carburetor  will  be  forced  into  the  water 
gas  as  the  latter  passes  through  the  intermediate  chamber 
between  carburetor  and  superheater,  and  the  oil  and 
water  gas  will  be  thoroughly  incorporated  in  the  super- 
heater. By  other  arrangements  of  the  valves,  the  tem- 
perature of  all  parts  of  the  apparatus  may  be  completely 
controlled. 

When  the  coal  becomes  cooled  below  the  proper  tem- 
perature, air  is  again  blown  through  it  and  out  through  0 
and  the  entire  process  just  described  is  repeated.  The 
steam  is  blown  up  through  the  coal  at  the  beginning  of 
the  "  run  "  and  down  through  it  during  the  latter  part. 

SUMMARY 

Petroleum  is  an  oily  liquid  found  in  the  earth  and  is  a  complex 
mixture  of  hydrocarbons. 

Refining  of  Petroleum  consists  in  the  fractional  distillation  of  the 
crude  petroleum  and  the  removal  of  impurities  from  the  fraction- 
ated portions.  The  products  include  light  and  solvent  oils  like 
petroleum  ether,  naphtha,  benzine,  and  gasoline  ;  burning  oils  like 
kerosene ;  light  and  heavy  lubricating  oils ;  and  waxes  of  varying 
hardness. 

Destructive  Distillation  is  the  breaking  up  of  a  complex  substance 
by  heating  without  access  of  air,  into  a  number  of  simple  sub- 
stances which  are  evaporated  and  then  condensed. 

Destructive  Distillation  of  Wood  yields  tar  and  tarry  oils,  pyro- 
ligneous  acid,  combustible  gas,  and  a  residue  of  charcoal.  From 
the  pyroligneous  acid  wood  alchohol,  acetone,  and  acetic  acid  are 
obtained. 


EXERCISES  383 

Turpentine  is  one  of  the  products  of  the  destructive  distillation 
of  resinous  woods. or  of  the  pitch  obtained  from  resinous  trees. 

Destructive  Distillation  of  Soft  Coal  yields  illuminating  gas,  am- 
moniacal  liquor,  coal  tar,  and  a  residue  of  coke.  Ammonia  is 
extracted  from  the  ammoniacal  liquor  and  many  valuable  carbon 
compounds  from  the  coal  tar.  Several  impurities  must  be  re- 
moved from  illuminating  gas  before  it  is  fit  for  burning. 

Water  Gas  is  made  by  steam  passing  through  incandescent  hard 
coal  or  soft  coke,  and  is  enriched  by  incorporating  oil  gases  of 
high  illuminating  power  with  it.  The  process  of  manufacture  is 
intermittent. 

EXERCISES 

1.  What  is  petroleum?     What  are  "  oil  sands"?     What 
is  meant  by  "  shooting  a  well "  ? 

2.  What  is  a  crude  oil  still  ?     How  is  it  heated  ?     What 
is  left  in  it  at  the  end  of  a  distillation  ? 

3.  Show  how   the  construction  of  the  cobblestone  tower 
makes  it  a  more  efficient  condenser  than  the  rectangular  tower. 

4.  Why  do  the  cobblestone  and   rectangular  towers  have 
discharge  pipes  at  both  the  top  and  the  bottom  ? 

5/  Why  is  cold  water  kept  circulating   in   tank  D  (Fig. 
101)  ?     Why  do  not  the  pipes  run  straight  through  ? 

6.  Describe  the  duties  of  the  "  still  man "  in  the  running 
house. 

7.  Why  are  some  of  the  condensed  vapors  from  the  crude 
oil  allowed  to  run  back  to  the  still  ? 

8.  What  is  accomplished  by  the  steam  stills  ?     How  do 
they  operate  ? 

9.  WThat  are  the  agitators?     In  purifying  the  fractional 
distillates,  what  is  the  use  of  the  sulphuric  acid,  the  sodium 
carbonate,  and  the  water  ? 

10.  Why  has  the  quality  of  commercial  gasoline  deterio- 
rated in  recent  years  ? 


384  PETROLEUM,    WOOD,   AND   COAL 

11.  What  is  meant  by  the  "  cracking  "  of  oils  ? 

12.  What  is  destructive  distillation  ? 

13.  What  is  pyroligneous  acid  ?  Charcoal  ? 

14.  Why  is  not  acetone  obtained  directly  from  the  destruc- 
tive distillation  of  wood  ?     Trace  the  commercial  process  for 
making  acetone  indirectly  from  wood. 

15.  Why  is  soft  coal  used  for  making  illuminating  gas  ? 

16.  What  are  the  three  main  steps  in  separating  the  prod- 
ucts leaving  the  retorts  in  a  coal  gas  plant  ? 

17.  Name  three  common  coal  tar  products. 

18.  Explain  the  use  of  the  fire  chamber,  the  carburetor,  and 
the  superheater  in  an  enriched  water  gas  plant. 

19.  Write  an  equation   for  the  preparation  of  unenriched 
water  gas.     What  is  "enriching"  and  how  is  it  accomplished? 

20.  Explain  why  the  enriched  water  gas  plant  described  is 
economical  in  space,  and  efficient  in  the  control  of  the  temper- 
ature of  all  parts  of  the  apparatus. 

21.  Why  is  soft  coal  not  used  in  a  water  gas  plant? 


CHAPTER   XXXIII 

BLAST  LAMPS  AND  BLOWPIPES 

372.  Blast  Lamps.  —  One  of  the  most  familiar  facts  re- 
garding combustion  is  that  the  greater  the  draft,  the  hot- 
ter the  fire.  The  blacksmith,  having  a  considerable  supply 
of  solid  fuel  in  the  forge,  increases  the  rapidity  with  which 
the  fuel  burns,  and  so  raises  the  temperature,  by  blowing 
a  blast  of  air  through  the  incandescent  coal  by  means  of 
his  bellows.  In  the  bunsen  burner,  as  has  already  been 
shown  (§  105),  the  air  is  drawn  in  through  the  ori- 
fices in  the  side  of  the  burner  tube  in  a  comparatively 
slow  stream.  The  resulting  flame  is  large  in  size  and  of 
moderately  high  temperature.  Now  the  amount  of  heat 
produced  when  a  cubic  foot  of  gas  is  burned  is  the  same, 
whether  it  burns  slowly  >or  rapidly  ;  but  the  temperature 
produced  is  much  greater  when  the  gas  burns  rapidly 
than  when  it  burns  slowly.  Therefore  if  either  gas,  air, 
or  both  are  supplied  to  the  burner  under  pressure,  so  that 
they  will  flow  to  the  flame  more  rapidly,  the  combustion 
will  be  more  rapid  and  the  temperature  higher.  The 
flame  will  also  be  smaller,  and  so  the  heat  will  be  concen- 
trated to  a  greater  extent. 

Gas  burners  to  which  one  or  both  of  the  gases  taking 
part  in  the  combustion  are  supplied  under  pressure  are 
called  blast  lamps  or  blowpipes.  A  simple  example  is 
found  in  the  laboratory  blast  lamp  (Fig.  104).  Gas  is 
brought  to  the  burner  through  one  of  the  rubber  tubes 
and  admitted  to  the  large  outer  tube  of  the  burner.  Air, 

385 


386 


BLAST  LAMPS  AND  BLOWPIPES 


FIG.  104. — LABORATORY  BLAST 
LAMP. 


supplied  under  pressure  from  a  bellows  or  an  air  com- 
pressor, is  brought  through  the  other  rubber  tube  and 

admitted  to  a  small  tube  placed 
in  the  center  of  the  large  tube. 
It  will  be  noticed  that  the  ar- 
rangement of  air  and  gas  in  the 
blast  lamp  [is  just  the  reverse 
of  that  in  the  bunsen  burner. 
The  proportion  of  gas  and  air 
supplied  to  the  burner  can  be 
regulated  by  means  of  the 
thumb-screws  shown  at  either 
side  of  the  burner.  In  oper- 
ation, the  gas  is  first  admitted 
and  lighted,  giving  a  large, 
sooty,  flickering  flame.  The 

air  is  then  turned  on ;  the  flame  becomes  much  smaller 
and  intensely  hot,  making  a  rustling  noise  as  it  burns.  A 
properly  adjusted  blast  lamp  has  a  flame  with  practically 
no  inner  cone.  The  narrowing  of  the  outer  tube  at  the 
tip  causes  the  gas  and  air  to  form  a  much  more  intimate 
mixture  than  is  obtained  in  the  bunsen  flame,  and  so  more 
uniform  combustion  and  a  higher  temperature  result. 
Blast  lamps  are  used  for  a  great  variety  of  operations  in 
which  a  temperature  higher  than  that  of  the  bunsen  flame 
is  required. 

373.  The  Blow  Torch,  used  by  plumbers,  painters,  and 
others,  is  essentially  similar  to  the  blast  lamp,  but  uses 
liquid  fuel.  The  gasoline,  or  kerosene,  is  forced  up  to 
the  needle  valve  (Fig.  105),  by  means  of  air  compressed 
by  a  pump  attached  to  the  torch.  The  needle  valve  causes 
the  fuel  to  flow  out  in  a  fine  spray,  which  is  easily  vaporized. 
To  start  the  torch,  a  little  fuel  is  allowed  to  run  out  into  the 


OXY-HYDROGEN  BLOWPIPE 


387 


heating  pan  just  below  the  burner,  the  needle  valve  is  closed 
and  the  fuel  in  the  pan  is  lighted.  The  flame  thus  produced 
heats  the  metal  parts  around  the  needle  valve,  and  when  the 
latter  is  again  opened,  the  issuing  spray  is  vaporized  and 
so  is  easily  ignited.  When  the  torch  is  burning,  the  parts 
surrounding  the  needle  valve  remain  hot  enough  to  con- 


FIG.  105.  —  BLOW  TORCH:  «,  NOZZLE;  v,  VALVE. 

tinue  to  vaporize  the  fuel  as  fast  as  it  is  furnished,  as  in 
the  case  of  the  gasoline  stove  and  gasoline  torch  (§§  110 
and  115).  The  air  needed  for  combustion  in  the  torch  is 
drawn  in  through  openings  in  the  sides  or  bottom  of  the 
shield  surrounding  the  needle  valve,  as  in  the  case  of  the 
bunsen  burner.  In  the  blow  torch  it  is  the  fuel  vapor 
which  is  furnished  under  pressure. 

374.  Oxy-hydrogen  Blowpipe.  —  The  intense  heat  of  the 
hydrogen  flame  has  already  been  noted  (§  4).  The 
maximum  temperature  of  this  flame  can  be  obtained  by 
using  a  mixture  of  2  volumes  of  hydrogen  to  1  of  oxygen 
—  the  proportion  in  which  the  two  gases  unite  to  form 
water.  As  this  mixture  of  hydrogen  and  oxygen  is 
highly  explosive,  special  precautions  must  be  taken  in 
burning  it.  The  oxy-hydrogen  blowpipe  (Fig.  106)  is 


388  BLAST  LAMPS  AND  BLOWPIPES 

constructed  on  the  same  principle  as  the  blast  lamp.     The 
hydrogen  is  lighted  first  and  burns  in  air,  then  the  oxygen 

Q      is  turned  on.      Both  gases 

^^ '     for  this  blowpipe   are  al- 
ways used  under  pressure. 
I  Hydrogen  There    are   three  reasons 

for  this.  In  the  first 
FIG.  106. — •  OXY-HYDROGEN  BLOWPIPE. 

place,  the  rapidity  of  burn- 
ing is  increased  by  compressing  the  gases  and  the  temper- 
ature of  the  flame  correspondingly  increased.  Secondly, 
the  rapidity  with  which  the  gases  escape  from  the  burner 
prevents  the  flame  from  traveling  back  toward  the  hydro- 
gen supply  and  causing  a  disastrous  explosion.  Thirdly, 
it  is  more  convenient  to  store  highly  compressed  gases 
than  gases  under  lower  pressure,  which  consequently 
occupy  a  larger  volume. 

By  the  oxy-hydrogen  blowpipe,  temperatures  of  from 
2000°  to  2500°  C.  can  be  reached,  the  limiting  temperature 
being  determined  by  the  temperature  at  which  the  water 
formed  in  the  process  begins  to  dissociate  again  into  hy- 
drogen and  oxygen,  absorbing  heat  in  so  doing.  The 
temperatures  obtained  are  sufficient  to  melt  platinum  and 
silica  (§  474)  and  the  oxy-hydrogen  flame  is  employed 
for  these  purposes.  Another  important  use  of  the  oxy- 
hydrogen  flame  is  in  the  calcium  or  lime  light,  in  which 
the  flame  is  directed  against  a  stick  of  lime  or  calcium 
oxide  (Fig.  4,  page  5).  The  lime  is  heated  to  a  brilliant 
white  heat,  and  is  used  as  the  source  of  light  for  stereop- 
ticons  and  theatrical  spot  lights.  For  both  of  these  pur- 
poses the  calcium  light  has  given  place  to  the  electric  arc, 
wherever  electric  current  can  be  obtained.  The  oxy- 
hydrogen  flame  is  also  employed  in  lead  burning,  that  is, 
the  joining  of  sheets  or  other  pieces  of  lead  by  melting 
their  edges  together. 


OX  Y-A  CE  T  YLENE  EL  O  WPIPE 


389 


375.  Oxy-acetylene  Blowpipe.  —  The  intense  heat  of  the 
oxy-acetylene  flame  has  been  known  for  a  long  time. 
With  the  improvement  in  the  commercial  manufacture  of 
acetylene,  the  oxy-acetylene  blowpipe  has  been  developed 
until  it  has  become  an  exceedingly  useful  tool.  By  its 
use,  two  pieces  of  metal  of  almost  any  kind  can  be  joined 
completely  by  fusing  them  together  at  the  junction,  and 
wrought  iron  and  steel  can  be  cut  rapidly  and  with  great 
convenience. 

A  complete  oxy-acetylene  outfit  is  shown  in  Fig.  107. 
At  the  left  is  seen  the  acetylene  generator,  in  the  center, 


FlG.     107. OXY-ACETYLENE    BLOWPIPE   OUTFIT. 

the  oxygen  tank,  and  in  the  workman's  hand  is  the  blow- 
pipe or  "torch"  with  which  the  work  is  done.  The 
acetylene  generator  has  already  been  described  (§  99). 
The  oxygen  is  compressed  into  strong  steel  tanks.  The 
blowpipe  is  constructed  on  the  same  general  principles  as 


390  BLAST  LAMPS  AND  BLOWPIPES 

the  oxy-hydrogen  blowpipe,  but  is  somewhat  more  com- 
plicated. It  will  be  remembered  that  acetylene  cannot  be 
safely  compressed  as  a  gas  to  any  considerable  extent,  but 
that  acetone  will  dissolve  several  times  its  own  volume  of 
acetylene,  which  can  then  be  liberated  under  pressure 
from  the  acetone.  On  these  facts  depend  the  construc- 
tion of  two  types  of  blowpipes,  the  low-pressure  and  the 
high-pressure. 

In  the  low-pressure  blowpipe,  the  oxygen  is  supplied 
under  a  pressure  of  15  to  25  pounds  per  square  inch 
and  the  acetylene  usually  at  less  than  1  pound.  The 
oxygen  is  carried  to  the  working  end  of  the  blowpipe 


FIG.  1,08. — OXWELD  Low  PRESSURE*  BLOWPIPE. 

(Fig.  108),  through  a  tube  extending  through  the  center  of 
the  handle  to  a  fine  opening  (a)  at  the  base  of  the  nozzle. 
The  acetylene,  passing  through  the  outer  chamber  of  the 
handle,  enters  a  space  surrounding  the  oxygen  jet.  The 
shape  of  the  passages  in  the  nozzle  is  such  that  the  oxy- 
gen draws  the  acetylene  rapidly  into  the  nozzle  and  the 
gases  are  thoroughly  mixed  before  they  reach  the  tip  of 
the  blowpipe,  from  which  they  issue  at  high  speed.  The 
pressure  of  the  oxygen .  can  be  adjusted  by  a  reducing 
valve  on  the  oxygen  tank,  and  the  amount  of  each  gas  is 
regulated  by  a  separate  stopcock.  The  danger  of  striking 
back  is  averted  by  the  velocity  with  which  the  gases  issue 
from  the  blowpipe,  and  also  by  a  wire  gauze  screen  (w)  in 


AUTOGENOUS    WELDING  391 

the  passage  at  the  base  of  the  nozzle,  because  a  flame  will  not 
pass  through  minute  holes.  The  blowpipe  just  described 
is  used  for  fusing  and  welding  only.  The  cutting  nozzle 
will  be  described  later. 

For  emergency  repairs  and  other  cases  where  it  is  not 
convenient  to  transport  the  bulky  acetylene  generator,  a 
cylinder  of  acetone  saturated  with  250  times' its  volume 
of  acetylene  under  a  pressure  of  150  pounds  per  square 
inch  is  used.  In  this  case,  a  different  form  of  nozzle  is 
employed.  The  low-pressure  system,  however,  is  cheaper, 
and  is  used  if  possible. 

The  complete  combustion  of  acetylene  to  carbon  dioxide 
and  water  would  require  2.5  volumes  of  oxygen  to  1  of 
acetylene.  But  the  parts  of  the  oxy -acetylene  apparatus 
are  designed  so  that  the  acetylene  breaks  up  at  the  tip  of 
the  blowpipe  into  carbon  and  hydrogen.  Only  the  carbon 
burns,  while  the  hydrogen  surrounds  the  flame  and  acts  as 
a  protection  against  oxidation  of  the  metal.  The  tempera- 
ture of  the  flame  is  above  the  temperature  at  which  water 
dissociates  into  hydrogen  and  oxygen,  and  so  the  hydro- 
gen does  not  burn  at  the  jet,  but  only  on  the  outside  of 
the  flame. 

376.  Autogenous  Welding.  —  When  two  pieces  of  metal 
are  joined  by  running  liquid  metal  of  similar  character 
on  the  surfaces  to  be  united,  the  process  is  called  autoge- 
nous welding.  An  example  is  lead  burning.  The  oxy- 
acetylene  blowpipe,  producing  a  temperature  of  nearly 
4000°  C.,  is  peculiarly  adapted  to  autogenous  welding  of 
even  the  less  fusible  metals,  like  iron  and  steel.  In  the 
case  of  thin  sheets  of  metal,  the  edges  are  brought  into 
perfect  contact  and  then  fused  together,  without  the  ad- 
dition of  other  metal.  In  most  cases,  however,  a  space  is 
left  between  the  pieces  and  into  this  space  is  run  fused 


392 


BLAST  LAMPS  AND  BLOWPIPES 


metal  of  the  same  kind,  suitable  to  produce  a  weld  that 
can  be  machined.  The  operator  in  Fig.  107  is  melting  the 
stick  of  metal  which  he  holds  in  his  left  hand  for  this 
purpose.  This  metal  used  as  a  "  filler  v  should  be  rich  in 
the  easily  oxidizable  constituents  of  the  metal  to  be 
welded.  It  is  necessary  also  to  use  suitable  fluxes  for  the 
removal  of  oxides  from  the  molten  metal,  and  to  regulate 
the  gases  in  the  blowpipe  so  that  the  inner  zone  of  the 
flame  shall  be  neither  oxidizing  nor  reducing  in  its  action. 
In  welding  all  but  thin  metal,  the  adjacent  metal  is  pre- 
heated, so  that  when  the  entire  piece  cools  after  the  ad- 
dition of  the  molten  metal,  it  shall  be  free  from  strains. 
Preheating  lessens  the  time  of  blowpipe  heating  and  so 

saves  gas.  Blaugas  and 
oxygen  are  also  used  for 
autogenous  welding 
(Fig.  109)  and  for  cut- 
ting. 

The  applications  of 
autogenous  welding  are 
very  numerous.  It  is 
used  as  a  substitute  for 
riveting  in  the  manufac- 
ture of  steel  and  iron 
tanks.  The  parts  of 
bicycle  frames  and  other 
articles  made  of  steel 
tubing,  safes,  and  steel 
office  furniture  are  welded  in  this  way.  It  is  the  means 
employed  in  the  manufacture  of  aluminum  articles 
whenever  it  is  necessary  to  join  two  parts,  as,  for  instance, 
welding  the  spouts  into  aluminum  teakettles.  A  most 
important  application  is  in  repair  work.  Here  it  is  used 
to  fill  in  holes  in  defective  castings,  which  would  other- 


FIG.  109. 


OXY-BLAUGAS  -WELDING 
OUTFIT. 


CUTTING  39S 

wise  have  to  be  remade,  to  repair  broken  machine  parts 
and  to  build  up  worn  ones,  and  in  the  repair  of  aluminum 
gear  cases  and  other  automobile  parts. 

377.  Cutting.  —  Another  important  use  of  the  oxy-acety- 
lene  flame,  combined  with  a  high-pressure  oxygen  blast, 
is  in  cutting  iron,  steel,  and  other  metals.  The  cutting 


FIG.  110. — STEEL  CUT  WITH  OXY-ACETYLENE  FLAME. 


blowpipe  has  a  circle  of  small  oxy-acetylene  jets  at  its 
point,  while  in  the  center  is  an  opening  for  oxygen  at 
high  pressure.  The  small  jets  are  turned  on  first,  and 
serve  to  heat  the  metal  intensely.  When  the  metal  has 


394  BLAST  LAMPS  AND  BLOWPIPES 

been  heated  to  about  1000°  C.,  the  jet  of  oxygen  at  high 
pressure  is  turned  on.  This  oxidizes  the  metal,  and  the 
force  of  the  jet  blows  out  the  molten  oxide  as  rapidly  as 
it  is  formed,  thus  making  a  comparatively  narrow  cut. 
After  the  cut  is  started,  the  small  oxy-acetylene  flames 
aid  the  process  by  helping  to  bring  the  metal  up  to  its 
kindling  temperature,  for  the  cutting  process  really  con- 
sists in  burning  the  iron  or  steel.  Cast  iron  cannot  be 
cut  by  this  process,  but  wrought  iron,  structural  steel, 
armor  plate,  and  many  special  steels  that  cannot  be  cut 
with  tools  yield  to  the  combination  of  intense  heat  and 
abundant  oxygen.  The  process  is  of  great  service  in 
cutting  up  scrap  iron  and  steel,  in  wrecking  steel  struc- 
tures, in  trimming  steel  castings,  and  in  trimming  away 
defective  parts  preparatory  to  welding.  In  much  of  this 
work,  a  perfectly  even  cut  is  not  necessary  and  the  blow- 
pipe is  guided  by  hand.  By  using  proper  mechanical 
means  for  guiding  the  torch,  very  even  cuts  of  any  form 
can  be  made  (Fig.  110). 


SUMMARY 

Blast  Lamps  are  burners  in  which  an  intimate  mixture  of  gas 
and  air  issues  from  the  burner  with  great  velocity  and  burns  with 
a  hot,  non-luminous  flame.  They  are  used  in  laboratories  and 
wherever  a  small  flame  having  a  high  temperature  is  required. 

Blow  Torches  are  blast  lamps  adapted  to  the  use  of  liquid  fuel. 

The  Oxy-hydrogen  Blowpipe  is  a  burner  in  which  oxygen  and 
hydrogen,  both  highly  compressed,  unite  and  burn  with  an  intensely 
hot  flame.  It  is  used  for  melting  platinum  and  silica,  for  the  cal- 
cium light,  and  for  fusing  together  the  edges  of  sheets  of  lead  and 
other  metals. 

The  Oxy-acetylene  Blowpipe  is  similar  in  construction  to  the 
oxy-hydrogen  blowpipe.  It  employs  acetylene  in  place  of  hydrogen 


EXERCISES  395 

and  produces  a  hotter  flame.     It  is  used  for  the  autogenous  weld- 
ing of  many  metals. 

Metals  may  be  cut  by  burning  them  with  a  jet  of  high  pressure 
oxygen,  provided  they  are  heated  at  the  same  time  with  an  oxy- 
acetylene  flame. 

EXERCISES 

1.  Compare  the  blast  lamp  with  the  bunsen  burner  as  to 
(a)  construction,   (b)    rapidity   of    combustion,    (c)    tempera- 
ture produced. 

2.  Why  do  blast  lamps  and  blowpipes  have  an  outer  and 
an  inner  tube  ? 

3.  Why  is  the  outer  tube  narrowed  at  the  end  ? 

4.  Give  the  order  of  operations  in  lighting  a  blast  lamp, 
with  the  reason  for  following  this  order. 

5.  Why  has  the  flame  of  the  blast  lamp  very  little  inner 
cone? 

6.  Describe  the  lighting  of  a  blow  torch,  stating  reasons  for 
each  operation. 

7.  Compare   the   oxy-hydrogen   blowpipe   with   the    blast 
lamp  as  to  (a)  construction,  (b)  temperature  produced,  (c)  uses. 

8.  Explain  what  is  meant  by  autogenous  welding,  and  give 
examples  of  its  use. 

9.  What  is  "  preheating,"  and  what  is  its  purpose  in  autog- 
enous welding  ? 

10.  Explain  how  an  oxy-acetylene  cutting  blowpipe  differs 
from  a  welding  blowpipe. 

11.  What  two  purposes  does  the  high-pressure  oxygen  jet 
serve  in  oxy-acetylene  cutting  ? 


CHAPTER   XXXIV 

GAS  ENGINES 

378.  Construction  and  Operation.  —  The  use  of  gaseous 
fuels  as  sources  of  light  and  heat  has  been  followed  in 
recent  years  by  their  extensive  use  for  power.  The  gas 
engine  consists  essentially  of  a  cylinder  in  which  a  mix- 
ture of  gas  and  air  burns  explosively.  The  combustion 
raises  the  temperature  of  the  gases  in  the  cylinder  and  so 
causes  them  to  exert  a  powerful  pressure  against  a  pis- 
ton. The  motion  of  this  piston  is  transmitted  to  a  crank 
and  flywheel  by  a  connecting  rod.  The  cylinder  is  pro- 
vided with  valves  for  admitting  gas  and  air,  and  for  per- 
mitting the  products  of  combustion  to  escape.  The  mix- 
ture of  gas  and  air  is  ignited  at  the  proper  point  in  the 
stroke  by  raising  a  small  portion  to  its  kindling  point, 
usually  by  an  electric  spark.  The  combustion  takes  place 
in  from  T^  to  -ffa  of  a  second. 

Starting  with  the  combustion  of  the  charge,  which  takes 
place  with  the  piston  ready  to  begin  its  forward  stroke, 
the  order  of  events  in  a  "  four-cycle  "  engine  is  as  follows : 

(1)  the  pressure  suddenly  produced  by  the  burning  of 
the  mixture  drives  the  piston  forward  to  the  end  of  its 
stroke  (power  stroke)  ; 

(2)  the  energy  stored  in  the  flywheel  forces  the  piston 
back  and  the  burned  gases  are  expelled  through  an  ex- 
haust valve  (exhaust  stroke)  ; 

(3)  the  piston  is  again  drawn  forward  by  the  flywheel 
and  fresh  supplies  of  air  and  gas  are  drawn  in  through 

396 


USE    OF   GAS   ENGINES 


397 


valves  which  open  at  the  beginning  of  the  stroke  (admis- 
sion stroke)  ; 

(4)  the  flywheel  again  forces  the  piston  back  to  the 
starting  position  and  compresses  the  new  mixture  before 
it  is  ignited  (compression  stroke). 


Admission  Stroke 


Compression  Stroke 


Power  Stroke 


Exhaust  Stroke 


4  1  2 

FIG.   111.  —  GAS  ENGINE  CYCLE. 

In  this  type  of  engine  there  is  only  one  power  stroke  in 
two  revolutions,  but  the  pressure  developed  is  so  high 
that  the  heavy  flywheel  easily  carries  the  engine  through 
the  other  three  strokes.  The  cylinder  walls  are  made 
hollow,  so  water  can  be  kept  circulating  between  to  pre- 
vent overheating. 

379.  Use  of  Gas  Engines.  —  Gas  engines  found  their  first 
extensive  commercial  use  in  the  oil  fields,  where  natural 
gas,  associated  with  petroleum  in  origin,  frequently  flows 
from  the  ground  in  large  quantities.  This  gas  has  high 
heating  power  and  consists  chiefly  of  marsh  gas,  together 


398  GAS  ENGINES 

with  some  hydrogen  and  other  combustible  gases.  Thus 
the  oil  producer  is  often  enabled  to  pump  his  wells  with- 
out paying  any  fuel  bills.  The  fact  that  in  internal-com- 
bustion engines  like  the  gas  engine,  the  heat  is  used 
directly  at  the  point  where  it  is  produced,  led  the  oil  pro- 
ducer to  use  a  gas  engine  instead  of  burning  the  gas  under 
the  boiler  of  a  steam  engine.  This  greater  efficiency  of 
the  gas  engine,  and  its  greater  convenience  of  operation 
as  compared  to  the  steam  engine,  soon  led  to  the  adoption 


FIG.   112.  —  LARGE  GAS  ENGINE  FOR  POWER  PLANT. 

of  the  gas  engine  for  use  with  illuminating  gas  for  small 
power  plants,  although  the  usual  price  of  gas  was  too 
high  to  permit  its  economical  use  for  large  plants.  The 
question  of  expense  is  now  met  by  individual  gas  plants 
for  each  power  plant,  because  about  twice  as  much  power 
can  be  produced  from  a  ton  of  coal  by  means  of  a  gas 
producer  and  a  gas  engine  as  by  a  steam  boiler  and  steam 
engine. 

380.  Gas  Producers.  — The  gas  producer  (Fig.  113)  is  not 
unlike  an  ordinary  coal  stove  in  its  construction  and  action. 
It  is  a  vertical  closed  cylinder  containing  a  deep  bed  of  coal, 
resting  on  a  bed  of  ash.  The  coal  is  lighted  at  the  bottom 


GAS  PRODUCERS 


399 


and  a  carefully  regulated  jet  of  air  is  blown  through  the 
coal.     At  the  bottom  of  the  producer,  the  carbon  in  the 
coal  is  burned  to  carbon 
dioxide: 


C 

carbon 


02 

oxygen 


C02 

carbon 
dioxide 


As  this  gas  passes  up 
through  the  incandescent 
coal  above,  it  is  reduced  to 
carbon  monoxide: 


CO, 


c 


-2  CO 

carbon 
monoxide 


FIG.  113. —  GAS  PRODUCER. 


'2       + 

carbon  carbon 

dioxide 

This     carbon     monoxide, 
with  some  hydrogen  and 
hydrocarbons,        together 
with  the    nitrogen  of  the  original  air,  constitute  "  pro- 
ducer gas." 

About  6  %  of  steam  is  often  mixed  with  the  air  in  the 
blast.  This  steam  increases  the  amount  of  combustible 
material  in  the  gas,  as  it  reacts  with  the  coal  to  form 
carbon  monoxide  and  hydrogen,  both  of  high  fuel  value: 

4-    C  — >-  CO     +    H9 


H20 

water 


carbon 


carbon 
monoxide 


hydrogen 


The  difference  between  the  action  with  steam  and  with 
air  is  that,  in  the  case  of  the  steam,  there  is  no  non-com- 
bustible gas,  like  nitrogen,  remaining,  and  also  the  pro- 
ducer may  be  operated  at  a  lower  temperature. 

When  bituminous  coal  is  used,  tjie  percentage  of  hydro- 
carbons is  much  higher  than  with  hard  (anthracite)  coal, 
and  the  heating  power  of  the  gas  and  the  efficiency  of  con- 
version of  the  coal  into  gas  is  higher.  From  82  %  to  87  % 


400  GAS  ENGINES 

of  the  energy  contained  in  the  original  coal  is  left  in  the 
producer  gas.  This  gas  is  used  in  the  regular  way  in  the 
gas  engine.  The  application  of  producer  gas  and  of  waste 
gases  from  blast  furnaces  and  coke  ovens,  have  made  prac- 
tical the  development  of  high  power  gas  engines. 

381.  Combustion  in  the  Engine.  — The  proportions  of  gas 
and  air  that  give  the    best  results   in  the  engine  range 
from  6  of  air  to  1  of  gas,  which  gives  about  the  highest 
pressure  at  the  instant  of  combustion,  to  8  of  air  to  1  of 
gas,  which  is  the  best  working  pressure  under  ordinary 
conditions,  as  the  combustion  continues  through  a  larger 
portion  of  the  stroke  with  the  latter  mixture.     With  a 
proper  mixture  of  gas  and  air,  the  products  of  combustion 
are  non-poisonous  gases,  which   are   exhausted   into   the 
atmosphere.     The  reactions  of  the  oxygen  of  the  air  with 
the  most  important  constituents  of  the  gas  (carbon  mon- 
oxide, hydrogen,  and  marsh  gas),  are  shown  in  the  follow- 
ing equations : 

2  CO    +     O2      —^2  CO2 

carbon  carbon 

monoxide  dioxide 

2  H2    +     02     —^2  H20 

hydrogen       oxygen  water 

CH4    +  2  02  — >•  C02  +  2  H20 

.       methane         oxygen  dioxide  water 

382.  Gasoline   and   Kerosene   Engines.  —  The    vapors    of 
liquid  fuels,  such  as  gasoline  and  kerosene,  are    exten- 
sively used  in  internal-combustion  engines.     The  auto- 
mobile has  brought  the  gasoline  engine  to  a  high  degree 
of  perfection.     The  gasoline  engine  differs  from  the  gas 
engine  only  in  the  fact  that  gasoline  vapor  is  used  instead 
of   gas.      The  gasoline  is  introduced  in  drops  or  a  fine 


SUMMARY  401 

spray  into  the  carburetor,  which  is  a  heated  chamber 
where  it  is  mixed  with  air  and  is  vaporized.  The  gasoline 
engine,  as  employed  in  the  aeroplane,  represents  a  maxi- 
mum of  power  with  a  minimum  of  space  and  weight. 


FIG.   114. — AUTOMOBILE  ENGINE  —  4-CvLiNDER. 

Kerosene  oil  is  also  used  in  engines  similar  in  construc- 
tion to  the  gas  engine.  It  is  usually  introduced  as  a  spray 
directly  into  the  cylinder,  whose  walls,  heated  from  the 
previous  charge,  vaporize  the  oil.  The  heat  generated  by 
the  compression  of  the  charge  is  sufficient  to  ignite  it,  so 
the  electric  spark  is  not  necessary. 

SUMMARY 

The  Gas  Engine  derives  its  power  from  the  explosive  combustion 
of  a  mixture  of  gas  and  air  in  the  cylinder. 

The  combustible  mixture  is  (a)  introduced  into  the  cylinder, 
(b)  compressed,  (c)  ignited,  and  (d)  the  burned  gases  are  driven 
out. 

About  six  times  as  much  air  as  gas  is  required  for  the  most 
efficient  operation  of  the  gas  engine. 

In  Gas  Producers,  a  partial  combustion  of  coal  takes  place,  re- 
sulting in  the  formation  of  carbon  monoxide.  Steam  is  sometimes 
mixed  with  the  air  used  in  producers ;  in  that  case,  hydrogen  as 


402  GAS  ENGINES 

well  as  carbon  monoxide  is  produced.  A  ton  of  coal  furnishes 
more  energy  when  used  with  a  gas  producer  and  gas  engine  than 
when  used  with  a  boiler  and  steam  engine. 

Liquid  Fuels  may  be  used  in  internal  combustion  engines,  by 
being  first  converted  into  a  vapor  or  spray. 

EXERCISES 

1.  Give  an  example,  other  than  a  gas  engine,  of  energy 
directly  produced  by  the  burning  of  an  explosive  mixture. 

2.  During  what  fraction  of  the  time  that  a  gas  engine  is 
running  is  power  being  exerted  on  the  flywheel  ? 

3.  What  advantage  has  a  four-cylinder  automobile  engine 
over  a  single-cylinder  eugine  of  the  same  power? 

4.  Write  equations  showing  the  formation  of  producer  gas 
when  a  mixture  of  air  and  steam  is  used. 

5.  What  advantages  result  from  the  use   of   bituminous 
rather  than  anthracite  coal  in  a  gas  producer  ? 

6.  Write  equations  to  show  the  composition  of  the  exhaust 
from  a  gas  engine,  taking  gas  from  a  gas  producer  using  steam 
and  air. 

7.  What  proportions  of  air  and  gas  are  most  efficient  in  a 
gas  engine  ?     Why  ? 

8.  Why  must  liquid  fuels  be  vaporized  or  converted  into  a 
spray  before  they  are  used  in  internal-combustion  engines  ? 

9.  What  results  from  feeding  too  much  gasoline  to  an  auto- 
mobile engine  ? 

10.   Explain,  with  diagrams,  the  operation  of  a  four-cycle 
engine. 


CHAPTER   XXXV 

EXTRACTION  OP  METALS 

383.  Minerals  and  Ores.  —  A  mineral  is  an  inorganic  sub- 
stance of  definite  chemical  composition  found  in  the  earth. 
A  mass  of  any  one  mineral  of  sufficient  extent  to  be  an 
important  source  of  an  element  is  seldom   found  pure. 
The  natural  deposits  from  which  the  elements,  especially 
the  metals,  are  extracted  are  termed  ores.     An  ore  generally 
consists  of  a  mineral  containing  the  desired  element,  mixed 
with   undesirable  substances   which  must   be  eliminated 
during  the  process  of  extraction.     To  use  a  common  illus- 
tration, large   quantities  of  iron   are   obtained   from   the 
mineral  hematite  (ferric  oxide).     Hematite  is  commonly 
found  mixed  with  sand  and  other  substances  which  must 
be  eliminated  during  the  process  of  extracting  the  iron. 
The  mixture  of  ferric  oxide  with  other  materials  constitutes 
an  important  ore  of  iron. 

384.  Carbonates  as  Ores.  —  All  common  carbonates,  with 
the  exception  of  sodium  carbonate  and  potassium  carbonate, 
when  heated,  decompose  before  they  melt,  yielding  carbon 
dioxide  and  a  metallic  oxide.     Carbon  dioxide,  being  a  gas, 
escapes  and  leaves  the  non-volatile  metallic  oxide  behind. 
Some  of  the  metallic  carbonates  are  important  ores.     In 
order  to  separate  metals  from  them,  they  are  frequently 
heated  to  convert  them  into  oxides,  which  are  subsequently 
reduced  by  heating  with  a  reducing  agent.     For  example, 
zinc  oxide  is  obtained  from  zinc  carbonate,  iron  oxide  from 
iron  carbonate,  and  copper  oxide  from  copper  carbonate. 

403 


404  EXTRACTION  OF  METALS 

When  any  one  of  these  oxides  is  heated  with  carbon  as  a 
reducing  agent,  usually  in  the  form  of  coke  or  charcoal, 
the  carbon  combines  with  the  oxygen  of  the  metallic  oxide 
and  leaves  the  metal  behind.  The  two  steps  of  the  process 
may  be  carried  on  in  one  operation. 

ZnCO3   —  >-    CO2      +     ZnO 

zinc  carbon  zinc 

carbonate  dioxide  oxide 

ZnO      +        C    —  >-      CO         +     Zn 

zinc  carbon  carbon  zinc 

oxide  monoxide 


385.  Sulphides  as  Ores.  —  When  the  ore  is  a  sulphide,  it 
is  roasted,  that  is,  heated  in  air  to  bring  about  some  desired 
chemical  change.  If  the  metal  contained  in  the  ore  does 
not  form  an  oxide  readily,  or  if  its  oxide  is  easily  decom- 
posed by  heat,  the  metal  may  be  obtained  directly  from  the 
roasted  ore.  Mercury  is  obtained  in  this  way  from  its 
principal  ore,  mercuric  sulphide  or  cinnabar.  When  the 
mercuric  sulphide  is  heated  in  contact  with  air,  the  com- 
bined sulphur  is  oxidized  to  sulphur  dioxide,  whicli  escapes 
as  a  gas.  The  oxide  of  mercury  does  not  appear  because 
it  is  readily  decomposed  by  heat.  Mercury  passes  off  as 
a  vapor  which  is  readily  condensed,  and  is  thus  separated 
from  the  more  volatile  sulphur  dioxide,  and  from  the  non- 
volatile constituents  of  the  ore: 

HgS    +    02    —  *-   S02    +     Hg 

mercuric          oxygen  sulphur         mercury 

sulphide  dioxide 

In  the  case  of  metals  whose  sulphides  oxidize  readily, 
roasting  is  often  employed  to  free  the  ore  from  the  com- 
bined sulphur  and  to  convert  the  metal  into  an  oxide.  The 
metallic  oxide  may  be  desired  for  commercial  use,  or  it 
may  be  reduced  in  order  to  obtain  a  metal: 


ALUMINUM  405 

2  ZnS   +     3  O2   — •>•  2  SO2     +     2  ZnO 

zinc  oxygen  sulphur  zinc 

sulphide  dioxide  oxide 

ZnQ  +     C        — »-     CO      +  Zn 

zinc  carbon  carbon  zinc 

oxide  monoxide 

386.  Use    of    Electricity.  —  Metals    such    as*  aluminum, 
sodium,  potassium,  magnesium,  and  calcium,  whose  oxides 
cannot  be   economically   reduced,   are   obtained   by   elec- 
trolytic processes. 

387.  Aluminum  is  one  of  the  metals  prepared  on  a  large 
scale  by  electrolysis.     The  process  should  be  of  interest  to 
American  boys  on  account  of  its  invention  by  an  American 
youth  just  out  of  college.     Charles  M.  Hall  was  graduated 
from  Oberlin  College  in  1885.     He  invented  the  process 
at  present  employed  for  the  manufacture  of  aluminum  in 
1886,  when  he  was  in  his  twenty-second  year.     The  form  of 
apparatus  employed  has  been  perfected  since  that  time,  but 
the  method  remains  fundamentally  unchanged.    The  pro- 
cess invented  in  this  country  by  Hall  and  that  invented  in- 
dependently in  France  by  Heroult  are  practically  the  same. 
What  the  invention  of  these  men  has  meant  commercially 
is  shown  by  the  fact  that  in  1889,  just  before  the  Hall 
process  was  placed  on  a  commercial  basis,  aluminum  sold 
for  |4  a  pound,  while  at  present  the  price  of  aluminum  is 
about  20  cents  a  pound  in  ingot  form. 

Bauxite,  an  ore  containing  from  50  %  to  70  %  of  alumina 
(aluminum  oxide),  is  the  chief  source  of  alumina.  In  re- 
fining the  bauxite,  advantage  is  taken  of  the  fact  that  alu- 
mina forms  with  soda  a  compound  known  as  sodium  alumi- 
nate,  Na3AlO3,  which  is  soluble  in  water.  The  impurities 
in  bauxite  are  insoluble  or  nearly  so.  The  sodium  alumi- 
nate  formed  by  the  action  of  soda  with  bauxite  is  separated 


406  EXTRACTION  OF  METALS 

from  its  impurities  by  filtering.  The  sodium  aluminate  in 
the  filtrate  is  decomposed,  the  aluminum  being  thrown  out 
of  the  solution  as  a  hydrate.  This  hydrate  is  heated  in  a 
furnace  for  48  hours  at  temperatures  which  gradually  reach 
1100°  C.  This  drives  off  water  from  the  hydrate  and  leaves 
it  in  the  form  of  alumina  ready  to  be  used  in  the  aluminum 
furnace. 

Aluminum  oxide  is  a  very  stable  compound  and  cannot 
be  reduced  by  heating  with  carbon.  When  heated  with 
carbon  in  an  electric  furnace,  aluminum  carbide  is  obtained. 
Its  fusion  point  is  so  high  that  the  melting  of  alumina  on 
a  large  scale  is  practically  impossible.  Since  alumina  is 
insoluble  in  water,  some  other  solvent  must  be  sought  for 
the  electrolytic  bath. 

Cryolite  (3  NaF  .  A1F3)  is  a  mineral  having  a  low  melt- 
ing point,  but,  when  melted,  is  a  very  poor  conductor  of 
electricity.  Now,  aluminum  oxide  is  readily  soluble  in 
molten  cryolite  and  the  solution  is  a  good  conductor  of 
electricity.  On  the  passage  of  the  current  through  the 
solution  of  alumina  in  molten  cryolite,  the  aluminum  oxide 
is  decomposed,  aluminum  being  liberated  at  the  cathode 
and  oxygen  at  the  anode.  Hall  made  use  of  such  an  elec- 
trolysis for  the  preparation  of  aluminum. 

388.  Commercial  Extraction  of  Aluminum.  —  The  appara- 
tus (Fig.  115)  employed  for  the  commercial  extraction  of 
aluminum  consists  of  an  iron  box>  about  8  feet  long,  4  feet 
wide,  and  2  feet  deep,  lined  with  a  thick  layer  of  carbon 
which  serves  as  the  cathode.  Carbon  rods  about  3  inches 
in  diameter  are  used  as  anodes.  About  40  carbon  rods  are 
used  in  one  piece  of  apparatus. 

An  artificial  mixture  of  fluorides,  containing  the  fluorides 
of  sodium,  calcium,  and  aluminum,  is  placed  in  the  appara- 
tus and  the  carbon  rods  are  jammed  against  the  bottom  of 


COMMERCIAL   EXTRACTION  OF  ALUMINUM     407 

the  apparatus.  On  the  passage  of  the  electric  current,  the 
rods  become  heated  and  the  mixture  of  fluorides  melts. 
The  rods  are  then  raised  slightly  from  the  bottom  of  the 
box  and  alumina  is  added.  The  aluminum  oxide  is  de- 


FIG.   115.  —  ELECTROLYTIC  EXTRACTION  OF  ALUMINUM. 

composed,  as  described  above,  and  the  aluminum  collects 
in  the  lower  part  of  the  box,  from  which  it  is  drawn  from 
time  to  time, by  removing  a  wooden  plug  from  the  taphole. 
The  oxygen  which  appears  at  the  carbon  anodes  oxidizes 
them  so  that  the  amount  of  carbon  consumed  about  equals 
the  weight  of  the  aluminum  obtained.  A  layer  of  coke  is 
spread  over  the  top  of  the  molten  mass,  to  prevent  radia- 
tion and  to  protect  the  workman's  eyes.  The  aluminum 
oxide  is  placed  on  the  layer  of  coke  and  dries  before  it 
is  stirred  into  the  bath. 

As  the  amount  of  alumina  in  solution  decreases,  the  re- 
sistance of  the  bath  increases.  This  fact  is  made  use  of 
to  operate  a  signal  which  calls  the  attention  of  the  opera- 
tor to  the  fact  that  the  bath  needs  attention.  Alumina  is 
added  by  stirring  in  some  of  that  which  has  been  drying 
on  the  coke.  During  the  electrolysis  the  resistance  of  the 


408  EXTRACTION  OF  METALS 

bath  is  sufficient  to  generate  enough  heat  to  keep  the  bath 
in  a  molten  condition. 

Aluminum  is  at  present  one  of  the  common  metals  and 
is  extensively  employed  for  making  cooking  utensils,  elec- 
tric cables,  and  valuable  alloys. 

389.  Thermit. —  The  fact  that  aluminum  is  a  far  more 
powerful  reducing  agent  than  carbon  was  discovered  by 
Prof.  Hans  Goldschmidt  of  Essen.  At  pvesent,  the  Gold- 
schmidt  Thermit  Company  is  making  practical  use  of  this 
important  discovery  for  the  extraction  of  the  formerly 
expensive  metals  manganese  and  chromium  from  their 
oxides,  for  the  production  of  many  valuable  alloys,  and  for 
the  production  of  molten  iron  at  a  temperature  sufficiently 
high  to  weld  broken  parts  of  machinery  and  steel  rails. 

When  a  mixture  of  granulated  aluminum  and  ferric 
oxide  is  ignited,  the  aluminum  burns  very  rapidly  and 
takes  oxygen  from  the  ferric  oxide,  reducing  it  to  iron. 
The  energy  of  the  reaction  is  so  great  that  a  temperature 
of  3000°  C.  is  produced.  The  use  of  another  oxide,  or  of 
other  oxides,  in  place  of  the  ferric  oxide  makes  possible 
the  preparation  of  the  metals  manganese  and  chromium: 

3  MnO2    +     4  Al      — >-  2  A12O3  +     3  Mn 

manganese  aluminum  aluminum         manganese 

dioxide  oxide 

Valuable  alloys,  such  as  ferrotitanium,  chromium-copper, 
and  manganese-boron  are  prepared  by  the  Thermit  process. 
Since  the  apparatus  and  the  material  necessary  to  weld 
together  broken  parts  of  large  machines  occupy  little  space 
and  can  be  easily  transported,  the  Thermit  process  has 
become  of  great  value  for  making  repairs  in  cases  where 
the  removal  of  the  broken  part  would  cause  much  delay  and 
great  expense.  The  Thermit  process  of  welding  is  carried 
on  essentially  as  follows : 


THERMIT 


409 


A  crucible  shaped  furnace  (Figs.  116,  117)  is  charged 
with  a  mixture  of  granulated  aluminum  and  ferric  oxide,  to 
which  an  alloy  may  be  added  to  give  the  union  the  desired 


FIG.  116. — THERMIT  CRUCIBLE  FOR  WELDING. 

strength.     On  top  of  the  charge  is  placed  a  small  amount 

of  an  ignition  mixture,  consisting  of  magnesium  powder 

mixed     with     barium     peroxide.      The 

pieces   of   the    broken  part  are  brought 

into  alignment,  enough  metal  is  removed 

from    the    fractured    ends    to    permit  a 

free  flow  of  liquid  between  the  parts  to 

be  welded,  a  mold  is  built  around  the 

fracture,  and  the  ends  to  be  joined  are 

heated  by  a  gasoline  blow-torch.     The 

charged     crucible     is     placed     so    that  FIG.  117. 

molten  metal  can  be  delivered  from  it 

into  the  mold,  and  the  ignition  mixture  is  lighted  with  a 

match.     The  heat  generated  by  the  burning  ignition  mix- 


410  EXTRACTION  OF  METALS 

ture  sets  fire  to  the  crucible  charge.  The  aluminum  in 
burning  takes  oxygen  from  the  ferric  oxide  and  leaves 
molten  iron,  heated  to  a  temperature  of  3000°  C.,  on 
which  floats  aluminum  oxide.  The  molten  iron  is  then 
run  into  the  mold  surrounding  the  fracture.  The  ex- 


FIG.  118.  —  THERMIT  WELDING. 

tremely  hot  liquid  iron  flows  between  the  surfaces  to  be 
joined,  melts  some  of  the  metal  and  mingles  with  it,  so 
that  when  the  mass  cools,  the  pieces  of  the  broken  part 
are  united  by  metal  as  strong  as  that  of  which  the  ma- 
chine is  made.  This  process  is  one  of  the  methods  for 
autogenous  welding  (see  Chapter  XXXIII). 

390.  Gold  is  sometimes  found  free  in  sand  and  in  quartz 
rock.  To  separate  the  gold  from  such  mixtures,  the  mass 
in  which  it  occurs  is  pulverized  by  crushing,  if  necessary, 
and  the  gold  extracted  from  the  fine  material  by  one  of  the 
following  methods: 

1st.  When  gold  is  mixed  with  sand,  it  is  often  separated 
by  a  process  called  panning,  which  consists  in  agitating  the 
mixture  in  a  pan-shaped  vessel  filled  with  water.  The 
gold  settles  to  the  bottom  and  the  impurities  are  poured 
off  with  the  water. 

2d.  The  free  gold  is  amalgamated,  that  is,  dissolved  in 
mercury.  The  resulting  amalgam  is  then  mechanically 


GOLD  411 

purified,  and  the  gold  obtained  by  distilling  off  the  mer- 
cury. 

3d.  The  gold  is  dissolved  in  alkaline  cyanide  solutions 
in  the  presence  of  oxygen  or  an  oxidizing  agent,  as  shown 
by  the  equations: 

2Au  +  4KCN  +  2H20    +    O2—  ^ 

gold         potassium          water  oxygen 

cyanide 

2KAu(CN)2+2KOH    +    H2O2 

potassium  potassium  hydrogen 

aurocyanide  hydroxide  peroxide 

2  Au  +  4  KCN  +  H202  —  >-  2  KAu(CN)2  +  2  KOH 

gold         potassium      hydrogen  potassium  potassium 

cyanide          peroxide  aurocyanide  hydroxide 

From  the  potassium  aurocyanide  the  gold  may  be  precipi- 
tated by  zinc,  or  by  electrolysis. 

2  KAu(CN)2  +  Zn  —  ^  K2Zn(CN)4  +  2  Au 

potassium  zinc  potassium  gold 

aurocyanide  zinc  cyanide 

4th.  The  pulverized  ore  containing  the  gold  is  treated 
with  chlorine  to  form  auric  chloride,  which  is  soluble. 
The  solution  of  auric  chloride  may  be  treated  with  hydro- 
gen sulphide  to  form  the  insoluble  compound  auric  sul- 
phide. The  sulphide  is  then  separated  by  filtration  and 
decomposed  by  roasting. 


2  AuCl3  +  3  H2S  —  >-  Au2S3  +  6  HC1 

auric  hydrogen  auric  hydroge 

chloride          sulphide  sulphide         chloride 


Au2S3  +  3  O2  —  >-  3  SO2  +  2  Au 

auric  oxygen  sulphur     <     gold 

sulphide  dioxide 


412  EXTRACTION   OF  METALS 

391.  Complex  Ores.  —  Many  ores  are  complex  mixtures  of 
minerals  which  require  treatments  far  too  complicated  to 
be  understood  by  the  beginner. 

392.  Types  of  Furnaces.  —  Several  types  of  furnaces  are 
used  in  the  extraction  of  metals.      Among  these,  the  blast 
furnace,   the    reverberatory   furnace,   the    Bessemer    con- 
verter, the  open-hearth  furnace,  and  the  Goldschmidt  or 
"  Thermit "  furnace  are  of  great  importance.     The  first 
four  are  described  in  detail  in  Chapter  XL. 

393.  The   Reverberatory  Furnace     (Fig.    119)    is    used 
in  a  large  number  of  metallurgical  operations.     The  fire 
grate  is  placed  at  one  end  of  the  furnace  and  the  flame 

from  the  burning  fuel 
passes  just  under  the  roof 
and  over  the  furnace 
charge.  In  this  way  the 
carbon  from  the  fuel  is 
FIG.  119.  —  REVERBERATORY  FURNACE,  prevented  from  entering 

the    charge.      The    heat 

from  the  burning  gases  reverberates  back  and  forth  be- 
tween the  roof  and  the  charge.  A  reverberatory  furnace 
can  be  used  at  will  for  the  oxidation  or  the  reduction  of 
the  heated  material.  If  an  excess  of  air  is  allowed  to 
enter  the  furnace,  so  that  free  oxygen  passes  over  the 
bed,  oxidation  takes  place.  If,  on  the  other  hand,  an 
amount  of  air  less  than  that  required  for  the  complete 
combustion  of  the  fuel  gases  is  allowed  to  enter  the  fur- 
nace, oxygen  is  taken  from  the  charge,  which  is  thus 
reduced. 

394.  Extraction  of  Lead.  —  Lead  is  frequently  obtained 
from  ores  rich  in  the  sulphide  of  lead  (galena)  by  treat- 
ment in  a  reverberatory  furnace.     The  lead  sulphide  is  first 


EXTRACTION   OF   TIN  413 

heated  in  the  presence  of  an  excess  of  air  (roasted),  the  ore 
being  meanwhile  stirred  frequently.  By  this  process  a 
part  of  the  lead  sulphide  is  converted  into  lead  oxide, 
according  to  the  equation: 

2  PbS  +  3  O2  —  >-  2  PbO  +  2  SO2 

lead  oxygen  lead  sulphur 

sulphide  oxide  dioxide" 

Another  portion  6f  the  lead  sulphide  is  oxidized  to  lead 
sulphate,  as  shown  by  the  equation: 

PbS  +  2  O2  —  >-  PbSO4 

lead         oxygen  lead 

sulphide  sulphate 

At  the  end  of  the  roasting,  a  mixture  of  lead  oxide,  lead 
sulphate,  and  lead  sulphide  remains.  The  temperature  of 
the  furnace  is  then  raised  and  the  amount  of  oxygen  enter- 
ing the  furnace  is  reduced.  Under  these  conditions  the 
lead  sulphide  takes  oxygen  from  the  lead  oxide  and  lead 
sulphate,  as  shown  by  the  equations  : 

2  PbO  +  PbS  —  >-  S02  +  3  Pb 

lead  lead  sulphur         lead 

oxide          sulphide          dioxide 


PbS04  +  PbS-^2S02  +  2Pb 

lead  lead  sulphur         lead 

sulphate       sulphide          dioxide 

This  operation  will  be  seen  to  be  a  process  of  reduction,  in 
which  lead  sulphide  is  used  as  a  reducing  agent  to  remove 
oxygen  from  the  mixture.  As  the  lead  separates,  it  runs 
down  the  sloping  bed  of  the  furnace  and  is  removed.  The 
process  of  oxidation  and  reduction  are  alternately  repeated, 
and  fine  coal  is  added  to  complete  the  final  reduction. 

395.    Extraction  of  Tin.  —  The  extraction  of  tin  from  its 
chief  ore,  tin  oxide,  SnO2  (cassiterite),  is  often  carried  on 


414  EXTRACTION   OF  METALS 

in  a  reverberatory  furnace.  The  tin  oxide  is  mixed  with 
coal,  which  serves  as  the  reducing  agent. 

Sn02  +  2C— ^2  CO  +  Sn 

stannic        carbon  carbon          tin 

oxide  monoxide 

The  impure  tin  thus  obtained  is  slowly  heated  in  another 
reverberatory  furnace  so  that  the  pure  tin,  which  melts  at 
a  lower  temperature,  runs  off,  leaving  behind  a  less  fusible 
alloy  of  tin  with  iron,  arsenic,  etc. 


SUMMARY 

A  Mineral  is  an  inorganic  substance  of  definite  composition 
found  in  the  earth. 

An  Ore  is  a  more  or  less  pure  mineral  from  which  a  useful 
element  is  extracted. 

All  Common  Carbonates,  with  the  exception  of  the  carbonates  of 
sodium  and  potassium,  are  decomposed  by  heat  before  they  melt. 
Use  is  made  of  this  fact  in  the  preparation  of  calcium  oxide  from 
calcium  carbonate  and  in  the  conversion  of  several  carbonates 
into  oxides  preparatory  to  reduction  by  carbon. 

Sulphides. —  Mercuric  sulphide  when  roasted  in  air  is  converted 
into  sulphur  dioxide  and  mercury  vapor.  Many  sulphides  are 
converted  into  oxides  when  heated  in  air  and  the  oxide  is  then 
reduced. 

Electrolysis. — Sodium,  potassium,  magnesium,  calcium,  and 
aluminum  are  obtained  by  electrolysis.  Aluminum  is  obtained 
by  the  decomposition  of  aluminum  oxide  which  has  been  dis- 
solved in  a  mixture  of  molten  fluorides. 

Gold  is  separated  from  impurities  by  panning,  or  by  dissolving  it 
in  mercury,  or  in  a  solution  of  potassium  cyanide,  or  chlorine. 

Thermit  is  a  mixture  of  granulated  aluminum  with  one  or  more 
metallic  oxides.  It  is  used  in  smelting  manganese  and  chromium 


EXERCISES  415 

oxides,  in  the  preparation  of  various  alloys,  and  to  weld  broken 
castings  and  other  iron  and  steel  articles. 

A  Reverberatory  Furnace  has  the  fire  grate  at  one  end  of  the 
furnace  and  the  flames  pass  above  the  furnace  charge.  It  re- 
caives  its  name  from  the  fact  that  the  heat  reverberates  between 
the  roof  of  the  furnace  and  the  charge.  The  reverberatory  fur- 
nace is  used  in  the  smelting  of  certain  ores  of  tin,  lead,  and  cop- 
per, and  in  the  refining  of  iron  and  copper. 

EXERCISES 

1.  What  is  a  mineral?     How  does  a  mineral  differ  from 
an  ore  ? 

2.  Name  an  important  iron  mineral  and  an  important  iron 
ore. 

3.  Make  a  general  statement  concerning  the  decomposition 
of  carbonates  by  heat. 

4.  Name  three  carbonates  contained  in  important  ores. 

5.  How  could  zinc  be  obtained  from  zinc  carbonate  ? 

6.  Mention  three  sulphides  which  are  important   sources 
of  metals. 

7.  Why  is  not  mercuric  oxide  obtained  when  mercuric  sul- 
phide is  roasted  ? 

8.  What  processes  would  you  use  to  obtain  copper  from 
copper  sulphide  ? 

9.  Name  three  elements  which  are  obtained  by  electrolytic 
processes. 

10.  Give  a  description  of  the  Hall  process  for  the  manufac- 
ture of  aluminum. 

11.  In  the  Hall  process,  what  use  is  made  of  the  molten 
fluorides  ?     Of  the  aluminum  oxide  ?     What  becomes  of  the 
oxygen  liberated  during  the  process  ? 

12.  What  is  the  reducing  agent  most  frequently  used  in  the 
reduction  of  metallic  oxides  ? 


416  EXTRACTION    OF  METALS 

13.  How  are  manganese  and  chromium  obtained  from  their 
oxides  ? 

14.  What  reduction  takes  place  when  a  mixture  of  finely 
divided  aluminum  and  ferric  oxide  are  ignited  in  a  crucible  ? 
Give  the  equation. 

15.  Describe  the  Thermit  welding  process. 

16.  Define  an  amalgam.     How  is  gold  regained  from  gold 
amalgam  ? 

17.  What  would  happen  if  a  gold  ring  were  placed  on  some 
mercury  ? 

18.  Describe  briefly  a  process  by  which  gold  is  extracted 
from  an  ore. 

19.  How  can  lead  be  obtained  from  galena  ? 

20.  Name  an  important  ore  of  tin  and  describe  a  method  for 
extracting  tin  from  it. 


CHAPTER   XXXVI 
ELECTRIC  FURNACES      « 

396.  The  Conversion  of  Electricity  into  Heat  Energy  has  so 

many  applications  in  modern  chemical  operations  that  only 
a  few  of  the  more  important  ones  can  be  mentioned  in  a 
book  of  this  size.  Two  extensive  industries  of  American 
origin  are  the  manufacture  of  calcium  carbide  and  of  car- 
borundum. 

397.  Calcium  Carbide.  — In  1892,  Thomas  L.  Wilson,  while 
experimenting  at  Spray,  North  Carolina,  tried  to  produce 
calcium  by  the  reduction  of  calcium  oxide  by  carbon  in  an 
electric  furnace.     His  experiment  was  unsuccessful  so  far 


,.  ASBESTOS    BOARO\ 


FIG.  120.  —  LABORATORY  ELECTRIC  FURNACE. 

as  the  production  of  calcium  was  concerned,  but  from  it 
arose  an  unexpected  industry  of  great  importance.  It  is 
said  that  Wilson,  on  making  an  examination  of  the  contents 
of  the  furnace  at  the  close  of  the  experiment,  saw  that  he 
had  not  produced  calcium,  and  ordered  the  contents  of  the 
furnace  to  be  discarded.  The  workmen  threw  some  of  the 
material  into  a  near-by  stream  and,  much  to  the  surprise  of 
those  present,  a  gas  was  generated.  The  gas  was  found 

417 


418 


ELECTRIC   FURNACES 


to  burn  readily,  producing  a  very  smoky  flame.  Thus  was 
started  the  manufacture  of  calcium  carbide  on  a  large  scale. 
This  instance  serves  to  illustrate  the  many  cases  in  which 
scientific  investigation  has  not  reached  its  goal,  but  has 
resulted  in  an  unexpected  discovery  of  great  value.  Wil- 
son did  not  know  the  name  of  the  compound  which  he  had 
accidentally  discovered,  and  did  not  dream  of  the  important 


FIG.   121.  —  ROTARY  CARBIDE  FURNACE. 


FIG.  122. 


part  it  was  to  play  in  our  present  everyday  life.  A  con- 
sideration of  the  importance  of  calcium  carbide  for  use  in 
the  generation  of  acetylene  (§§  99,  119)  and  for  the  pro- 
duction of  calcium  cyanamide  (§  509)  will  give  the  reader 
some  idea  of  the  enormous  value  of  Wilson's  discovery. 

Calcium  carbide  can  be  readily  prepared  on  a  small 
scale  in  any  laboratory  provided  with  a  current  suitable 
for  operating  a  small  electric  furnace  such  as  is  repre- 
sented in  Fig.  120.  Calcium  oxide  and  a  good  grade  of 


CARBORUNDUM  OR   SILICON  CARBIDE         419 

carbon,  such  as  that  used  for  electric  light  carbons,  are 
finely  ground  and  thoroughly  mixed.  On  heating  the 
mixture  for  some  time  in  the  arc  of  the  furnace,  a  reaction 
takes  place  by  which  calcium  carbide  and  carbon  monoxide 
are  produced  according  to  the  equation : 

CaO    +    30    — •>-    CO    +    CaCa 

calcium        carbon  carbon          calcium 

oxide  monoxide        carbide 

Calcium  carbide  is  at  present  prepared  in  a  furnace 
similar  to  that  illustrated  in  Figs.  121,  122.  The  furnace 
consists  of  an  iron  wheel  (i?)  composed  of  insulated  seg- 
ments, to  which  can  be  attached  removable  cover  plates  (.A). 
The  mixture  of  coke  and  lime  is  delivered  from  the  bin 
(H)  to  the  hollow  space  between  the  grooved  wheel  and 
the  cover.  One  terminal  of  the  dynamo  (Z>)  is  connected 
to  the  graphite  electrode  ((7),  which  is  in  contact  with 
the  mixture  ;  the  other  terminal  is  connected  to  the  seg- 
ment of  the  wheel  containing  the  mixture,  by  means  of  a 
sliding  contact  on  the  commutator  (J^).  As  the  mixture 
is  converted  into  carbide,  the  wheel  is  rotated,  covers  at- 
tached where  needed,  and  fresh  mixture  supplied,  making 
the  process  continuous.  The  finished  carbide  is  removed 
at  the  opposite  side  of  the  wheel  at  (-F). 

398.  Carborundum  or  Silicon  Carbide.  —  E.G.  Acheson,  in 
1891,  while  trying  to  impregnate  clay  with  carbon  under 
the  influence  of  electric  heat,  obtained  a  small  'quantity  of 
a  beautiful,  crystalline  substance  which  was  found  to  rival 
the  diamond  in  hardness.  The  usefulness  of  this  new 
substance  as  an  abrasive  occurred  to  Acheson.  Believ- 
ing the  newly  discovered  substance  to  be  derived  from 
carbon  and  clay,  he  gave  it  the  name  of  carborundum. 
Later  investigations  showed  that  it  was  formed  by  a  reac- 
tion between  the  carbon  and  the  sand  (silicon  dioxide) 


420 


ELECTRIC  FURNACES 


mixed  with  the  clay.  Although  it  is  silicon  carbide,  SiC, 
it  still  retains  the  trade  name  carborundum.  Carborundum 
is  to-day  the  most  important  abrasive  on  the  market. 

Carborundum  is  prepared  by  heating  a  mixture  of  sand, 
coke,  salt,  and  sawdust  in  an  electric  furnace,  the  construc- 


FIG.   1 23.  —  CARBORUNDUM  FURNACE  —  SECTIONAL. 

tion  of  which  is  represented  in  Fig.  123.  Under  the  in- 
fluence of  the  high  temperature  produced  by  the  electric 
current,  the  sand  (silicon  dioxide)  and  coke  (carbon)  react 
as  shown  by  the  equation  : 


Si02 

silicon 
dioxide 


3C 

carbon 


2  CO   +   SiC 


carbon 
monoxide 


silicon 
carbide 


The  sawdust  is  used  because  when  heated  it  liberates  gases 
which  keep  the  mass  porous  so  that  the  carbon  monoxide 
can  escape  readily  and  burn  in  numerous  small  flames  at 
the  surface  of  the  mixture  (Fig.  124). 

Carborundum  is  so  hard  that  the  lumps  taken  from  the 
furnace  cannot  be  ground.  They  are,  however,  brittle  and 
are  readily  crushed  beneath  heavy  stone  wheels.  The 
coarser  portions  of  the  crushed  material  are  separated  into 
grains  of  a  definite  size  by  means  of  sieves,  while  the  finer 
portions  are  sorted  by  elutriation,  that  is,  by  the  rate  at 


ARTIFICIAL    GRAPHITE 


421 


which  they  sink  in  a  stream  of  running  water,  the  larger 
particles  being,  of  course,  the  first  to  settle. 

Carborundum,  in  a  great  variety  of  sizes,  is  sold  in  bulk. 
It  is  glued  to  cloth,  thus  making  a  substance  resembling 
emery  cloth,  or  sandpaper.  It  is  also  mixed  with  clay- 


FIG.  124.  —  ELECTRIC  CARBORUNDUM  FURNACE. 

like  substances,  and  the  mixture  is  molded  and  baked  in 
a  kiln.  In  this  way,  various  shaped  stones  suitable  for  all 
sorts  of  sharpening  and  grinding  work  are  made. 

399.  Artificial  Graphite.  —  The  use  of  the  electric  furnace 
for  the  manufacture  of  carborundum  led  to  the  discovery 
of  a  method  for  the  manufacture  of  artificial  graphite. 
Graphite  was  formed  in  the  hottest  part  of  the  carborun- 
dum furnace,  that  is,  next  to  the  core.  The  high  temper- 
ature decomposed  the  silicon  carbide  in  contact  with  the 
core,  the  silicon  -being  volatilized  and  the  carbon  deposited 


422  ELECTRIC  FURNACES 

in  the  form  of  graphite.  A  long  series  of  experiments 
convinced  Acheson  that  varieties  of  graphite  differing 
greatly  in  luster  and  unctuousness  can  be  produced  in  the 
electric  furnace,  and  that,  while  it  is  possible  to  make 
graphite  from  pure  carbon,  the  unctuous  varieties  of 
graphite  can  be  obtained  from  carbon  only  when  it  is 
mixed  with  mineral  matter  such  as  silica,  iron  oxid.e,  etc. 
The  impurities  probably  first  react  with  the  carbon  to 
form  carbides  which  subsequently  decompose. 


Copyright  by  the  International  Acheson  Graphite  Co. 

FIG.  125.  —  ELECTRIC  GRAPHITE  FURNACE. 

The  pulverized  coal  of  the  Pennsylvania  anthracite  coal 
mines  when  mixed  with  sand  and  heated  in  the  electric 
furnace  (Fig.  125)  yields  the  purest  quality  of  unctuous 
graphite.  Much  of  the  artificial  graphite  is  made  from 
such  material. 

Artificial  graphite  is  extensively  used  in  the  manufacture 
of  electrodes  and  in  the  preparation  of  lubricants.  Natural 
graphite  is  used  for  the  purposes  just  mentioned,  for  the 


LEAD  PENCILS  423 

making  of  crucibles  in  which  metals  are  to  be  melted,  for 
the  manufacture  of  the  leads  of  lead  pencils,  in  stove  and 
shoe  blacking,  and  for  lubricants  and  boiler  compounds. 

400.  Deflocculated  Graphite. — By  treating  finely  ground 
amorphous  or  non-crystalline  graphite  with  a  solution  of 
tannin  or   any  one  of   several  other  organic  substances, 
the  graphite  may  be  converted  into  particles  sufficiently 
fine  to  pass  through  filter  paper  and  to  remain  in  sus- 
pension when  mixed  with   water  or  with  oil.      Acheson 
calls  this  form  of  graphite  "  deflocculated  graphite."     De- 
flocculated  graphite  mixed  with  water  has  the  trade  name 
of  "  Aquadag,"  and  deflocculated  graphite  diffused  in  oil 
has  been  given  the  name  "  Oildag."     Aquadag  is  used  as 
an  aid  in  metal  cutting  and  Oildag  is  one  of  the  most 
valuable  lubricants  on  the  market.     By  mixing  a  cheap 
oil  with  graphite  a  product  can  be  obtained  which  is  equal 
to  a  high-grade  oil  for  use  as  a  lubricant. 

401.  Lead   Pencils.  —  In  the  manufacture  of    leads  for 
pencils,    the    graphite    is   first  separated    from   the   mica 
and  sand  with  which  it  is  found  mixed   in  the  natural 
deposits.      As  pure  graphite  is  too  soft  for  the  general 
requirements  of  a  pencil,  it  is  mixed  with  fine  clay  free 
from  particles  of  grit.     By  varying  the  amounts  of  clay 
and  graphite,  mixtures  of   various  hardness  can  be  ob- 
tained and  from  these  are  made  the  leads  for  the  great 
variety  of  pencils  on  the  market.     The  mixture  of  clay 
and    graphite    is    ground    in  water   between    millstones, 
passed   between   rolls   and   through    a   mixer,    and   then 
squeezed  through  a  die  to  form  a  rod  having  the  shape 
of  the  lead  of  the  pencil  to  be  made.     The  leads  after 
being   dried  are   subjected    to   a   temperature  of    about 
1100°  C.      The  heat  toughens  the  lead  so  it  is  ready  to 
be  placed  in  the  wood  of  the  pencil. 


424 


ELECTRIC  FURNACES 


402.  Carbon  Disulphide  (CS2)  is  a  very  volatile  liquid 
which  burns  in  a  manner  similar  to  gasoline.  The  ap- 
plication of  the  electric  fur- 
nace to  its  manufacture  is 
due  to  another  American, 
Edward  R.  Taylor.  The 
construction  of  the  furnace 
used  is  shown  in  Fig  126. 
As  no  air  can  be  permitted 
to  enter  the  furnace,  the 
electrodes  are  fixed  and  are 
prevented  from  wearing 
away  by  delivering  pieces 
of  carbon  over  their  ends. 
Part  of  the  heat  developed 
between  the  electrodes 
passes  to  the  walls  of  the 
furnace,  where  it  is  used  to 
melt  sulphur.  Within  the 
furnace  the  sulphur  vapor 
combines  directly  with  the 
carbon  as  shown  by  the 
equation  : 


MELTED  SULPHUR 

FIG.  126.  —  ELECTRIC  FURNACE  FOR 
MAKING  CARBON  DISULPHIDE. 


C    +    2S 

carbon        sulphur 


CS2 

carbon 
disulphide 


Carbon  disulphide  is  used  to  destroy  insects  of  various 
kinds  and  burrowing  animals,  such  as  moles,  woodchucks, 
etc.;  as  a  solvent  for  rubber  and  sulphur,  and  lately  large 
quantities  have  been  consumed  in  the  manufacture  of 
artificial  silk. 

403.  Electric  Smelting  and  Refining.  —  Recently  the  elec- 
tric furnace  has  been  introduced  as  a  source  of  heat  for  the 


ELECTRIC   SMELTING  AND  REFINING         425 

smelting  of  ores.     A  simple  form  of  a  furnace  designed  for 
the  smelting  of  tin  is  shown  in  Fig.  127. 


FIG.  127. —  FURNACE  FOR  SMELTING  TIN. 

A  furnace  invented  by  Heroult,  who  has  already  been 
mentioned  in  connection  with  Hall's  process  for  the  pro- 
duction of  aluminum  (§  387),  is  used  in  this  country  for 
the  production  of  high-grade  steel.  An  idea  of  the 
working  of  this  furnace  may  be  gained  from  Figs.  128, 
129  and  from  the  following  description.  The  furnace 
is  made  in  two  parts,  the  bed  and  the  roof,  which  are  so 
constructed  that  they  may  be  readily  separated.  It  is 
mounted  so  that  it  can  be  tipped  to  permit  the  charge  to 
run  out.  The  bed  of  the  furnace  consists  of  a  steel  shell 
lined  with  a  layer  of  fire  brick,  on  which  is  a  layer  of 
dolomite  (calcium  magnesium  carbonate).  The  cover  is 
made  of  iron  and  is  lined  with  fire  brick.  In  the  large 
Heroult  furnaces,  capable  of  treating  15  tons  of  steel  at 
a  time,  3  electrodes  are  used.  These  are  made  of  rods 
of  Acheson  graphite,  8  inches  in  diameter.  The  rods  are 
joined  so  as  to  form  one  rod  144  inches  long.  A  bundle 
of  3  of  the  long  rods  constitutes  one  electrode.  As  iron 
readily  combines  with  carbon  at  the  temperature  of  the 


426 


ELECTRIC   FURNACES 


furnace,  the  electrodes  are  not ,  permitted  to  touch  the 
steel.  They  dip  into  the  slag  which  floats  on  the  steel. 
The  slag  is  said  to  consist  of  magnetite  (Fe3O4)  and  a 
basic  flux,  the  former  being  used  as  an  oxidizing  agent 
and  the  latter  to  combine  with  the  sulphur  and  phospho- 


FIG.   128.  —  HEROULT  ELECTRIC  FURNACE  FOR  STEEL. 

rus  oxides  obtained  by  the  oxidation  of  the  sulphur  and 
phosphorus  in  the  impure  steel  or  iron.  The  electrodes 
are  automatically  regulated  so  that  their  ends  are  about  18 
inches  above  the  steel.  They  are  separated  so  that  the 
current  arcs  from  the  electrode  to  the  slag,  and  from  the 
slag  to  the  steel  underneath.  The  current  then  leaves  the 


ELECTRIC   SMELTING   AND   REFINING 


427 


furnace  by  arcing  from  the  steel  to  the  slag  and  from  the 
slag  to  the  electrode  by  which  it  returns  to  the  dynamo. 
An  alternating  cur- 
rent is  employed. 

The  Heroult  fur- 
nace has  been  proved 
to  be  of  great  value 
for  removing  unde- 
sirable elements,  sul- 
phur and  phospho- 
rus, from  a  low-grade 
Bessemer  steel,  thus 

producing      a      high      FlG>   129._HEROuLT  FURNACE  -  SECTIONAL. 
grade  steel.     In  gen- 
eral, the  furnace  provides  an  economical  means  for  the 
refining  of  steel. 


STEEL  SHELL 


SUMMARY 

Calcium  Carbide,  CaC2,  is  made  by  heating  in  an  electric  furnace 
ground  coke  and  lime  which  have  been  thoroughly  mixed.  The 
temperature  of  the  furnace  is  about  3000°  C.  Calcium  carbide 
is  extensively  used  for  the  production  of  acetylene,  and  increasing 
quantities  of  it  are  being  employed  in  the  production  of  calcium 
cyanamide.  » 

Carborundum,  silicon  carbide,  SiC,  is  made  by  heating  a  mix- 
ture of  coke,  sand,  sawdust,  and  salt  in  an  electric  furnace.  It 
closely  approximates  the  diamond  in  hardness  and  is  extensively 
employed  as  an  abrasive. 

Artificial  Graphite  is  prepared  by  heating  impure  carbon  in  an 
electric  furnace.  The  unctuousness  of  the  graphite  depends  on 
the  amount  of  silica,  ferric  iron,  and  other  mineral  matter  mixed 
with  the  carbon.  Much  artificial  graphite  is  made  by  heating  a 
mixture  of  silica  and  anthracite  culm.  Artificial  graphite  has 


428  ELECTRIC   FURNACES 

many  uses,  two  of  the  more  important  being  the  manufacture  of 
electrodes  and  lubricants. 

The  Lead  of  Lead  Pencils  consists  of  various  mixtures  of  graphite 
and  clay,  finely  ground  in  water  and  thoroughly  incorporated,  then 
molded,  dried,  and  subjected  to  a  high  temperature  to  harden 
them.  The  greater  the  percentage  of  clay  in  the  mixture  the 
harder  the  lead. 

Carbon  Disulphide  is  prepared  by  heating  carbon  and  sulphur  in 
an  electric  furnace  which  is  so  arranged  that  air  cannot  enter  it. 
Carbon  disulphide  is  used  as  an  insecticide,  as  a  solvent  for 
rubber,  and  in  the  manufacture  of  artificial  silk. 

The  Smelting  and  Refining  of  Metals  by  the  energy  derived  from 
the  electric  current  is  rapidly  increasing. 

EXERCISES 

1.  Briefly  tell  how  calcium  carbide  came  to  be  manufactured 
on  a  commercial  scale. 

2.  From  what  is  calcium  carbide  made  ?     Equation  ? 

3.  Mention  important  uses  of  calcium  carbide. 

4.  What  is  carborundum  ?     How  is  it  made  ?     Equation  ? 

5.  How  is  the  carborundum  that  comes  from  the  furnace 
converted  into  material  sufficiently  fine  for  use  as  an  abrasive  ? 

6.  How  are  carborundum  wheels  made  ? 

7.  What  led  to  the  discovery  of  artificial  graphite  ? 

8.  Upon  what  does  the  unctuousness  of  graphite  seem  to 
depend  ? 

9.  What  chemical  changes  probably  take  place  during  the 
formation  of  an  unctuous  graphite  ? 

10.  Mention  an  important  source  of  the  carbon  used  in  the 
manufacture  of  artificial  graphite. 

11.  What  are  some  of  the  uses  of  artificial  graphite  ? 

12.  Briefly  describe  the  making  of  the  lead  of  a  lead  pencil. 

13.  How  is  carbon  disulphide  made  ? 


EXERCISES  429 

14.  Why  is  it  necessary  to  prevent  air  from  entering  the 
carbon  disulphide  furnace  when  it  is  in  operation  ? 

15.  Why  is  great  care  taken  to  prevent  the  consumption  of 
the  electrodes  of  a  carbon  disulphide  furnace  ?     How  is  this 
accomplished  ? 

16.  For  what  purposes  is  carbon  disulphide  used? 

17.  Account  for  the  rapid  increase  in  the  use  of  the  electric 
current  for  metallurgical  operations. 

18.  Make  a  sectional  drawing  of  the  Heroult  furnace  for  the 
refining  of  steel. 

19.  Trace  the  path  of  the  current  through  the  Heroult  fur- 
nace. 

20.  What  becomes  of  the  impurities  in  the  unrefined  steel 
in  an  electric  furnace  ? 

21.  A  few  years  ago  many  predicted  that  the  open-hearth 
furnace  would  entirely  take  the  place  of  the  Bessemer  con- 
verter.    How  is  the  electric  furnace  likely  to  modify  this  pre- 
diction ? 


CHAPTER   XXXVII 

ELECTROCHEMISTRY 

404.  Development  of  Electrochemistry.  —  Every  improve- 
ment in  the  generation  of  electric  currents  has  been  fol- 
lowed by  a  great  extension  of  the  uses  of  electricity.     The 
growth  of  water-power  plants  for  generating  electricity, 
which  began  in  this  country  in  the  last  decade  of  the  nine- 
teenth century,  has  been  accompanied  by  the  development 
of  electrochemical  processes  for  the  manufacture  of  ma- 
terials formerly  prepared  in  other  ways  ;  by  the  application 
of  electrical  methods  to  the  extraction  and  refining  of 
metals  ;  and  by  the  separation  of  elements  and  the  produc- 
tion of  new  compounds,  which  electrical  processes  alone 
can  effect.     A  few  of  the  more  important  relations  between 
electricity  and  chemical  action  will  be  discussed  in  this 
chapter. 

405.  Conduction  of  Electricity.  --  There  are  two  classes  of 
substances  which  act  as  conductors  for  the  electric  current. 
The  first  class  includes  metallic  conductors,  such  as  copper, 
aluminum,  brass,  and  iron,  and  some  solid  non-metallic 
substances,  of  which  carbon  is  the  most  important.     The 
passage  of  a  current  through  these  conductors  is  not  ac- 
companied by  any  change  in  the  conductor,  other  than  the 
development  of  a  certain  amount  of  heat. 

Members  of  the  second  class  of  conductors  are  known  as 
electrolytes.  The  most  important  electrolytes  are  water 
solutions  of  acids,  bases,  and  salts.  Some  melted  com- 
pounds also  act  as  electrolytes.  The  passage  of  a  current 

430 


DISSOCIATION   THEORY  431 

through  an  electrolyte  is  accompanied  by  the  liberation  of 
two  different  substances.  One  of  these  appears  at  the 
terminal  where  the  current  enters  the  solution,  known  as 
the  anode,  or  +  electrode,  and  the  other  at  the  terminal  at 
which  the  current  leaves,  called  the  cathode,  or  —  electrode. 
For  example,  if  carbon  electrodes  are  placed  in  a  solution 
of  hydrogen  chloride  and  a  current  passed,  chlorine  gas  is 
liberated  at  the  anode,  and  hydrogen  at  the  cathode.  If 
sodium  chloride  is  used  instead  of  hydrogen  chloride, 
chlorine  is  liberated  at  the  anode  and  sodium  hydroxide  is 
found  in  the  solution  surrounding  the  cathode.  Before 
attempting  to  explain  this  result  it  will  be  necessary  to 
state  the  theory  of  electrolytic  dissociation. 

406.  Dissociation  Theory.  —  According  to  this  theory, 
when  an  electrolyte  is  dissolved  in  water,  a  portion  at  least 
of  its  molecules  break  up  into  two  parts,  one  charged  with 
positive  electricity  and  the  other  with  an  equal  amount  of 
negative  electricity.  These  charged  portions  of  the  mole- 
cule are  called  respectively  positive  and  negative  ion^ 
Thus,  when  sodium  chloride  is  dissolved  in  water,  an  equal 
amount  of  positive  sodium  ions  and  of  negative  chlorine 
ions  are  produced.  This  may  be  indicated  by  the  equation  : 

NaCl        ^"     Na+   +     Cl~ 

sodium  chloride  sodium         chlorine 

molecule  ion  ion 

Hydrochloric  acid  dissociates  in  solution  according  to 
the  equation : 

HC1         ±£      H+      +    Cl- 

hydrochloric  acid  hydrogen        chlorine 

molecule  ion  ion 

Sodium  hydroxide  dissociates  in  solution  as  follows : 
NaOH          ±^    Na+  +    OH~ 

sodium  hydroxide  sodium        hydroxyl 

molecule  ion  ion 


432  ELE  CTRO  CHEMIS  TR  Y 

It  will  be  noted  in  these  typical  examples  of  the  disso- 
ciation of  a  salt,  an  acid,  and  a  base,  that  the  hydrogen  ion 
and  the  metallic  ion  are  positive,  and  that  the  non-metallic 
ions  are  negative. 

In  a  solution  of  copper  sulphate  .there  are  copper  ions 
and  sulphate  ions : 

Cuso4   -*"7  GU++  +  scy- 

copper  sulphate  copper         sulphate 

molecule  ion  ion 

A  double  charge  is  indicated  here  on  each  ion,  as  the  num- 
ber of  charges  which  an  ion  carries  is  the  same  as  the 
number  expressing  its  valence  (§  50).  Molecules  of  the 
dissolved  substance  in  an  electrolyte,  then,  dissociate,  on 
dissolving,  into  positive  metallic  ions  and  negative  non- 
metallic  ions.  Hydrogen,  in  acids  and  acid  salts,  acts  as 
a  metallic  ion  ;  in  bases  it  is  a  part  of  the  complex  non- 
metallic  ion  OH~.  The  only  important  complex  positive 
ion  is  NH4+,  produced  by  the  dissociation  of  ammonium 
hydroxide  and  the  ammonium  salts. 

The  proportion  of  the  molecules  dissociated  at  a  par- 
ticular time  in  a  given  electrolyte  depends  on  the 
nature  of  the  dissolved  substance,  the  degree  of  dilution 
of  the  solution,  and  the  temperature.  Water  is  the  only 
important  solvent  in  which  any  considerable  amount  of 
dissociation  takes  place.  Many  soluble  substances,  par- 
ticularly organic  compounds  such  as  sugar,  alcohol,  and 
glycerin,  do  not  dissociate  on  dissolving.  Such  solutions 
are  known  as  non-  electrolytes  and  are  non-conductors  of 
electricity.  Pure  water  is  a  very  poor  conductor,  and 
therefore  its  molecules  are  only  slightly  dissociated. 

407.  Explanation  of  Electrolysis.  —  On  the  basis  of  the 
theory  just  stated  the  electrolysis  of  sodium  chloride  is 
easily  explained.  When  the  electrodes  are  dipped  into 


EXPLANATION   OF  ELECTROLYSIS  433 

the  solution  and  the  circuit  closed,  the  Na"1"  ions,  which 
have  been  moving  about  at  random  in  the  solution,  are 
immediately  repelled  by  the  positive  electrode  and  attracted 
by  the  negative  electrode,  since  like  electric  charges  always 
repel  and  unlike  charges  attract.  For  the  same  reason  the 
Cl~  ions  begin  to  move  toward  the  positive  electrode.  As 
soon  as  an  ion  reaches  the  electrode,  the  opposite  charges 
on  ion  and  electrode  neutralize  each  other.  The  chlorine 
ion,  losing  its  charge,  becomes  a  chlorine  atom ;  these 
unite  in  pairs  to  form  molecules.  When  a  sufficiently 
large  number  of  such  molecules  have  collected  at  the 
anode,  they  will  escape  from  the  solution  as  a  bubble  of 
chlorine  gas.  In  a  similar  way  the  sodium  ions  lose  their 
charge  at  the  cathode  and  become  sodium  atoms.  These 
do  not,  however,  unite  to  form  pieces  of  metallic  sodium, 
since  they  react  with  the  water  to  form  sodium  hydroxide  : 

2  Na  +  2  H20  — >-       2  NaOH       +       H2 

sodium  water  sodium  hydroxide          hydrogen 

Bubbles  of  hydrogen,  therefore,  will  escape  at  the  cathode. 
The  sodium  ion  did  not  react  with  the  water,  because  the 
presence  of  the  electric  charge  gives  the  ion  chemical 
properties  differing  from  those  of  the  atom. 

The  electrolysis  of  water,  described  on  page  3,  may 
now  be  explained.  It  was  there  stated  that  sulphuric  acid 
might  be  added  to  make  the  water  a  conductor.  Con- 
sidering the  action  first  as  an  electrolysis  of  sulphuric 
acid,  the  acid  dissociates  on  dissolving  in  the  water  into 
hydrogen  ions  and  sulphate  ions  : 

H2S04     :±5:      H+        +      H+      +     SO4— 

sulphuric  acid  hydrogen  hydrogen  sulphate 

molecule  ion  ion  ion 

As  the  current  passes,  the  ions  lose  their  charges  at  the 
electrodes.  At  the  cathode  hydrogen  ions  change  to 


434  ELECTROCHEMISTR  Y 

hydrogen  atoms  which  unite  to  form  molecules  of  hydro- 
gen. At  the  anode,  SO4 changes  to  SO4,  which  im- 
mediately reacts  with  the  water  as  follows  : 

S04    +   H20  — •*-  H2S04  +     O 

sulphate         .  water  sulphuric          oxygen 

radical  acid 

Thus  a  new  molecule  of  sulphuric  acid  has  been  produced 
in  place  of  the  one  originally  dissociated  and  an  atom  of 
oxygen  has  been  liberated.  The  oxj^gen  atoms  liberated 
at  the  anode  unite  to  form  oxygen  molecules,  which  escape 
as  a  gas.  The  entire  reaction  therefore  may  be  considered 
as  equivalent  to  that  shown  by  the  equation : 

2H20— ^     2H2      '+         02 

water  hydrogen  oxygen 

408.  Commercial  Electrolysis.  —  In  the  commercial  pro- 
duction of  hydrogen  and  oxygen  by  electrolysis,  a  solution 
of  caustic  potash,  KOH,  is  used  as  the  electrolyte.  The 
outer  iron  tank  (Fig.  131)  serves  as  the  negative  electrode 
and  a  perforated  inner  tank  made  of  iron  of  special  composi- 
tion is  the  positive  electrode.  These  electrodes  are  sepa- 
rated by  means  of  a  diaphragm  of  asbestos  (5"),  which 
permits  the  charged  ions  to  pass  freely,  but  prevents  the 
mixing  of  the  bubbles  of  liberated  gas.  A  hydraulic  joint 
(#)  also  prevents  the  mixing  of  the  liberated  gases,  and 
pressure  equalizers  on  top  (  (7)  deliver  the  gases  at  constant 
pressure  through  pipes  (^t,  B)  to  the  gas  holders  or  to 
compression  pumps,  for  compressing  it  into  cylinders. 

The  first  action  in  the  electrolysis  is  the  dissociation  of 
the  potassium  hydroxide  when  it  dissolves : 

KOH  ^±       K+         +'   OH- 

potassium  hydroxide  potassium  hydroxyl 

molecule  ion  ion 


COMMERCIAL   ELECTROLYSIS 


435 


When  the  potassium  ion  reaches  the  negative  electrode, 
it  loses  its  charge,  becomes  a  potassium  atom,  and  reacts 


FIG.  1  30.  —  ELECTROLYTIC 
GENERATOR  FOR  HYDROGEN 
AND  OXYGEN. 


FIG.  131.  —  ELECTROLYTIC  GENERATOR  — 
SECTIONAL.  D,  D,  ELECTRIC  TERMINALS. 
F,  FUNNEL  FOR  FILLING. 


with  the  water  of  the  solution,  forming  potassium  hydrox- 
ide again  and  liberating  hydrogen  : 

2  K     +  2  H2O  — +•         2  KOH          +      H2 

potassium         water  potassium  hydroxide          hydrogen 

The  hydroxyl  ions,  when  they  lose  their  charges,  react 
with  each  other,  forming  water  and  liberating  oxygen : 

OH    +    OH    — »-  H2O  +     O 

hydroxyl       hydroxyl  water         oxygen 

It  will  be  seen  that  the  net  result  of  these  reactions  is  the 
removal  of  one  molecule  of  water  from  the  solution  and 
the  liberation  of  two  atoms  of  hydrogen  and  one  atom  of 
oxygen.  So  it  is  only  the  water  in  the  cell  which  needs  to 
be  renewed  and  not  the  potassium  hydroxide. 


486  ELECTROCHEMISTRY 

The  hydrogen  produced  by  this  process  is  over  99  % 
pure  and  the  oxygen  more  than  98  %.  Where  electric 
current  is  obtained  cheaply  the  cost  of  this  process  of 
producing  oxygen  is  much  lower  than  that  of  the  potas- 
sium chlorate  process  usually  employed.  In  many  cases, 
the  hydrogen  produced  can  also  be  utilized  in  the  prepa- 
ration of  substitutes  for  lard,  an  industry  of  increasing 
importance  (§  210). 

409.  Explanation  of  Neutralization.  —  The  dissociation 
theory  offers  an  explanation  for  the  chemical  reactions  in 
which  solutions  of  acids,  bases,  and  salts  take  part.  In 
terms  of  this  theory,  an  acid  may  be  denned  as  a  com- 
pound whose  water  solution  contains  hydrogen  ions ;  a 
base,  as  a  compound  whose  solution  contains  hydroxyl 
(OH~)  ions ;  a  neutral  salt,  as  a  compound  whose  water 
solution  contains  positive  ions  from  a  base  and  negative 
ions  from  an  acid.  It  has  already  been  seen  (§  28)  that 
water  and  a  salt  are  the  products  of  neutralization.  Now 
water  is  only  very  slightly  dissociated  in  solution  and 
salts  are  very  highly  dissociated.  Therefore  if  a  solution 
containing  H+  ions  (an  acid)  is  mixed  with  a  solution 
containing  OH~  ions  (a  base),  there  will  be  a  decided 
tendency  for  each  pair  of  these  ions  to  unite  to  form  a 
molecule  of  water : 

H+     +   OH-  — >-   HOH 

hydrogen        hydroxyl  water 

ion  ion  molecule 

If  an  equation  for  neutralization  is  written  so  as  to 
show  the  ions  into  which  the  acid  and  the  base  dissociate, 
it  will  be  seen  that  the  simplest  reaction  possible  will  be 
the  union  of  the  positive  H+  ion  from  one  compound  with  the 
negative  OH~  ion  from  the  other,  since  the  unlike  charges  of 


OTHER   REACTIONS  BETWEEN  ELECTROLYTES    437 

these  ions  will  cause  them  to  attract  each  other.  The 
reaction  between  hydrochloric  acid  and  sodium  hydroxide 
solutions  will  serve  as  an  example  : 

H+    +    Cl-  +  Na+  4-    OH-—  >-HOH+  Na+  +   Cl~ 

hydrogen     chlorine       sodium      hydroxyl  water       sodium      chlorine 

ion  ion  ion  ion  molecule       ion  ion 

The  only  permanent  change  which  has  taken  place  is  the 
uniting  of  the  ions  H+  and  OH~  to  form  water.  The  ion 
Na+  and  Cl~  remain  in  solution  and  only  unite  to  form 
NaCl  on  evaporation.  Neutralization,  then,  is  essentially 
the  uniting  of  the  H+  ions  of  an  acid  with  the  OH~  ions 
of  a  base  to  form  undissociated  water.  The  equations 
for  other  neutralizations  will  show  that  the  formation  of 
undissociated  water  is  the  feature  common  to  them  all. 
For  example  : 


H+    +N03~+  K+  +  OH-  —  ^HOH+  K+   +  NO3~ 

hydrogen       nitrate       potas-     hydroxyl  water         potas-         nitrate 

ion  ion  sium  ion  molecule        sium  ion 

ion  ion 

2(H+)  +  SO4—  +  2(Na+)  +  2(OH~)  —>- 


hydrogen 
ions 

sulphate 
ion 

sodium 
ions 

hydroxyl 
ions 

2  HOH-f 

water 
molecules 

-  2(Na+)  H 

sodium 
ions 

sulphate 
ion 

410.  Other  Reactions  between  Electrolytes.  —  Many  reac- 
tions take  place  because  of  the  union  of  positive  ions  from 
one  compound  with  negative  ions  from  another  to  form  a 
compound  which  is  undissociated,  because  it  is  an  insol- 
uble solid.  The  use  of  silver  nitrate  as  a  test  for  the 
presence  of  a  chloride,  that  is,  of  the  Cl~"  ion,  is  an  ex- 
ample of  a  reaction  due  to  the  formation  of  an  insoluble 
compound.  Suppose  a  solution  of  sodium  chloride  (NaCl) 


438  ELECTROCHEMISTRY 

is  mixed  with  a  solution  of  silver  nitrate  (AgNO3).  The 
following  reaction  will  take  place : 

Na+  +  Cl-  +  Ag+  +  NO8-— >-  AgCl  +  Na+  +  NO3~ 

sodium      chloride        silver      nitrate        silver  chloride    sodium      nitrate 
ion  ion  ion  ion  molecule  ion  ion 

This  reaction  proceeds  to  completion  because  the  ions  Ag+ 
and  Cl~  unite  permanently  to  form  molecules  of  AgCl, 
which  will  not  again  dissociate,  because  they  are  insoluble. 
It  is  evident  that  any  soluble  chloride  would  behave  in  a 
way  similar  to  sodium  chloride,  because  its  solution  would 
contain  Cl~  ions.  As  all  nitrates  are  soluble,  their  solu- 
tions will  always  contain  positive  metallic  ions  and  NO3~ 
ions,  as  such. 

A  reaction  also  completes  itself  when  a  combination  of 
ions  produces  a  substance,  volatile  under  the  existing 
conditions.  The  ions  on  uniting  leave  the  solution  as 
undissociated  molecules  of  the  volatile  substance. 

411.  Primary  Cells.  —  The  production  of  electricity  in 
galvanic  batteries,  or  primary  cells,  is  the  result  of  the 
conversion  of  chemical  energy  into  electrical  energy.  A 
cell  consisting  of  a  zinc  plate  and  a  copper  plate,  immersed 
in  dilute  sulphuric  acid,  is  called  a  simple  cell  (Fig.  132). 
When  zinc  reacts  with  dilute  sulphuric  acid,  the  follow- 
ing action  takes  place : 

Zn  +  2(H+)  +  SO4~       — >-    Zn+  +  +  SO4~      +  H2 

zinc        hydrogen        sulphate  zinc  sulphate         hydrogen 

atom  ions  ion  ion  ion  molecule 

The  same  reaction  takes  place  between  the  zinc  plate  and 
the  acid  in  the  simple  cell.  The  zinc  plate,  before  immer- 
sion in  the  acid,  shows  no  trace  of  either  positive  or  negative 
electricity,  that  is,  the  positive  and  the  negative  electricity 
in  the  plate  are  just  equal  and  so  balance  each  other.  As 
the  zinc  ions  carry  their  positive  charge  with  them  from 


PRIMARY   CELLS 


439 


FIG.  132. 


the  zinc  plate  when  they  enter  the  solution,  they  leave  the 
plate  charged  with  negative  electricity.  Copper  does  not 
react  chemically  with  dilute  sulphuric 
acid.  As  the  Zn++  ions  repel  the  H+ 
ions  of  that  part  of  the  acid  which  has 
not  yet  come  in  contact  with  the  zinc 
plate,  these  H+  ions  will  move  away 
from  the  zinc  toward  the  copper  plate, 
constantly  repelling  the  H+  ions  which 
are  in  front  of  them.  The  result  is 
that  the  H+  ions  which  are  near  the 
copper  plate  will  come  in  contact  with 
that  plate.  They  then  give  up  their 
positive  charge  to  the  copper  plate  and 
unite  to  form  molecules  of  hydrogen.  The  copper  plate  is 
now  charged  positively  and  the  zinc  plate  negatively.  If 
the  plates  are  connected  by  a  wire  or  other  conductor,  the 
positive  and  negative  charges  will  pass  through  the  wire 

to  neutralize  each  other,  and 
this  constitutes  a  current  of 
electricity. 

Most  of  the  molecules  of 
hydrogen  liberated  at  the  cop- 
per cathode  of  the  simple  cell 
will  unite  to  form  bubbles  of 
hydrogen  gas,  which  escape  into 
the  air.  Some  of  the  hydro- 
gen, however,  adheres  to  the 
copper  plate,  arid  so  tends  to 
check  the  action  or  polarize  the  cell.  In  the  Daniell 
cell  polarization  is  prevented  by  surrounding  the  copper 
with  a  solution  of  copper  sulphate.  This  solution  is 
kept  separate  from  the  sulphuric  acid  by  placing  the  zinc 
and  sulphuric  acid  in  a  porous  cup,  while  the  copper  is 


CuSOi 
crystals 


FIG.   133.  —  GRAVITY  CELL. 


440  ELECTROCHEM1STR  Y 

immersed  in  the  copper  sulphate  solution  contained  in  the 
outer  vessel.  In  the  gravity  cell  (Fig.  133)  the  two  liquids 
are  separated  by  the  difference  in  their  specific  gravity.  In 
both  cells,  Cu++  ions  will  be  repelled  to  the  copper  plate 
instead  of  H+  ions,  and  so  no  polarization  will  take  place 
as  long  as  the  supply  of  copper  sulphate  is  maintained. 
The  "bluestone"  cells,  frequently  used  on  telegraph  lines, 
are  gravity  cells. 

412.  Sal  Ammoniac  Cells.  —  Another  cell,  which  is  more 
widely  used  than  either  the  simple  or  the  Daniell  cell,  is 
the  yal  ammoniac  cell.  The  electrodes  of  this  cell  are  zinc 
and  carbon,  and  the  electrolyte  is  a  solution  of  ammonium 
chloride  (sal  ammoniac).  The  reaction  which  takes  place 
is  : 

Zn  +    2(NH4+)    +   2(C1-)  —  >- 

zinc  ammonium  chlorine 

atom  ions  ions 


+     H2       +   2NH8 

zinc  chlorine  hydrogen         ammonia 

ion  ions  molecule         molecules 

This  equation  represents  the  final  result  of  the  action. 
It  is  altogether  probable  that  the  NH4+  ions  are  repelled 
by  the  Zn++  ions  as  these  enter  the  solution,  and  that  the 
following  reaction  takes  place  at  the  cathode  : 

2(NH4+)  —  s-  2NH3       +       H2 

ammonium  ammonia  hydrogen 

ions  molecules  molecule 

A  small  portion  of  the  ammonia  escapes,  but  the  greater 
part  dissolves  in  the  water.  As  in  the  case  of  the  simple 
cell,  hydrogen  may  accumulate  on  the  surface  of  the 
cathode  and  so  polarize  the  cell. 

The  cell  just  described  is  called  the  carbon  cylinder  cell. 
When  manganese  dioxide  is  present  as  a  depolarizer,  the 


SAL   AMMONIAC    CELLS 


441 


cell  is  called  the  Leclanche  cell  (Fig.  134).  The  manga- 
nese dioxide,  a  black  powder,  is  usually  mixed  with  gran- 
ulated carbon  to  increase  the  conduc- 
tivity, and  the  mixture  is  packed 
around  the  carbon  of  the  cell.  A  slow 
reaction  goes  on  in  the  presence  of 
hydrogen,  by  which  the  hydrogen  is 
oxidized  to  water  : 


2  MnO2 

manganese 
dioxide 


hydrogen 


Mn20,  - 

manganese 
trioxide 


H20 

water 


As  this  reaction  proceeds  slowly,  the 
cell  is  only  suitable  for  intermittent 
uses,  such  as  ringing  door  bells. 

In  recent  years,  the  Leclanche  cell  Fia  134.^— LECLANCHE 
has  been  largely  replaced  by  the  "dry" 
cell  (Fig.  135).  The  zinc  of  the  dry  cell  is  in  the  form 
of  a  can,  which  serves  as  a  container 
for  the  other  parts.  The  zinc  can 
(Z)  is  lined  with  absorbent  paper, 
such  as  blotting  paper,  which  is  satu- 
rated with  sal  ammoniac.  The  car- 
bon rod  (<7)  is  placed  in  the  center 
of  the  cell  and  the  space  between 
it  and  the  can  is  filled  with  a  mix- 
ture of  granulated  manganese  di- 
oxide and  graphite  (-27),  thoroughly 
wet  with  sal  ammoniac,  and  some- 
times with  other  chemicals.  The 
completed  cell  is  sealed  as  shown  at 
(P)  to  prevent  the  evaporation  of  the 
liquid.  It  is  evident  that  the  dry  cell  is  simply  a  modifi- 
cation of  the  Leclanche  cell.  The  dry  cell  is  more  com- 
pact and,  as  it  has  no  liquid  to  spill,  is  more  convenient 


FIG.  135.  —  DRY  CELL — 

SECTIONAL. 


442 


ELECTROCHEMISTRY 


than  the  Leclanche  cell,  particularly  where  it  must  be 
carried  in  various  positions,  as  in  the  ignition  battery  of 
an  automobile.  When  a  dry  cell  fails  to  act  further,  on 
account  of  the  exhaustion  of  the  electrolyte,  it  can  be  re- 
placed cheaply,  or  it  can  be  made  to  serve  some  time 
longer  by  punching  holes  through  the  zinc  and  placing 
the  whole  cell  in  a  jar  containing  sal  ammoniac  solution. 

413.  Storage  Cells.  —  Zinc,  which  is  the  positive  plate  of 
most  important  primary  cells,  is  used  up  in  the  production 
of  current,  and  the  frequent  replacement  of  the  zinc  makes 

these  cells  an  expensive 
source  of  current,  when 
much  is  required.  In 
the  secondary  or  stor- 
age cells  the  positive 
plate  is  a  compound 
which  gives  up  one  of 
its  elements  to  the  elec- 
trolyte while  the  cell  is 
furnishing  current  (dis- 
charging), and  later  has 
this  element  restored 


FIG.  136.  —  CHLORIDE  ACCUMULATOR  STOR- 
AGE BATTERY,  SHOWING  NEGATIVE  AND 
POSITIVE  PLATES  PARTLY  SEPARATED, 
WITH  CONTAINING  JAR  BEHIND. 


to  it  by  passing  a  cur- 
rent from  another 
source  through  the  cell 
(charging). 

The  lead  storage  battery  is  the  most  familiar  type  (Fig. 
136).  In  a  common  commercial  form  of  this  battery, 
the  positive  plate  consists  of  a  framework  or  grid  of  lead, 
in  the  spaces  of  which  is  packed  lead  peroxide  (PbO2). 
The  negative  plate  is  another  grid  of  lead,  with  its  pockets 
packed  with  finely  divided  or  spongy  lead.  The  electro- 
lyte is  dilute  sulphuric  acid.  The  probable  chemical  re- 


STORAGE   CELLS 


443 


action  that  takes  place  when  the  cell  is  furnishing  current 
(discharging)  is : 


PbO 


lead  oxide 
plate 


2  H2S04 

sulphuric  acid 
electrolyte 


2  PbSO 


lead  sulhate 


2H20 

water 


Pb 

lead 
plate      plate       electrolyte       both  plates 

That  is,  each  of  the  plates  tends  to  become  coated  on  the 
surface  with  lead  sulphate.  As  this  action  proceeds,  the 
electromotive  force  of  the  cell  remains  practically  con- 
stant for  a  considerable  time,  and  then  gradually  dimin- 
ishes, because  the  two  plates  are  becoming  alike. 

The  cell  is  then  charged,  by  connecting  it  to  some  other 
electric  generator  and  allowing  a  current  to  pass.  This 
current  causes  electrolysis  and  the  final  result  is  the 
reversal  of  the  reaction  given  above,  so  .that  the  equation 
for  charging  is  : 

2  PbSO4  +  2  H2O  — >-  Pb    +    PbO2  +  2  H2SO4 

lead  sulphate  water  lead  lead  oxide        sulphuric  acid 

both  plates  plate  plate  electrolyte 

Charging  and  discharging  can  be  repeated  a  large  number 
of  times  before  the  gradual  disintegration  of  the  plates 
makes  it  necessary  to  replace  them.  As  a  considerable 
amount  of  gas  passes  off  during 
the  process  of  charging,  it  is 
necessary  to  add  water  fre- 
quently and  sulphuric  acid 
occasionally.  Some  of  the  well- 
known  commercial  forms  of  this 
cell  are  the  "  Chloride  Accumu- 
lator "  and  the  "  Exide  "  cells. 

The  weight  of  the  lead  stor- 
age battery  and  the  mechanical 
weakness  of  its  plates  has  con- 
siderably limited  its  use.     The  Edison  storage  battery  is 
much  lighter  and  stronger  for  the  same  capacity.     Both 


FIG.     137.  —  PLATES    OF    THE 
EDISON  STORAGE  BATTERY. 


444  ELECTROCHEMISTR  Y 

plates  (Fig.  137)  are  of  nickel-plated  steel,  with  the 
active  material  contained  in  perforated  pockets.  In  the 
positive  plate,  the  active  material  is  nickel  peroxide  and 
in  the  negative  plate  it  is  finely  divided  iron.  The  elec- 
trolyte is  a  solution  of  caustic  potash.  During  discharge, 
the  iron  is  oxidized  and  the  nickel  peroxide  is  partly 
reduced.  The  reaction  is  reversed  in  charging.  At  the 
positive  plate,  the  equation  is: 

discharging 

Ni02  +  2(K+)   +   H20  ^±  NiO   +   2  KOH 

charging 

nickel          potassium          water  nickel  potassium 

peroxide  ions  oxide  hydroxide 

The  arrow  shows  in  which  direction  the  reaction  is  pro- 
ceeding during  the  charging  and  the  discharging  of  the 
cell.  At  the  negative  plate  the  reaction  is: 

discharging 

Fe   +   2(OH-)  ^  FeO   4-   H2O 

charging 

iron  hydroxyl  iron  water 

ions  oxide 

In  both  of  these  cells,  during  discharge,  chemical  energy 
is  being  converted  into  electrical  energy;  this  chemical 
energy  must  be  restored  to  the  cell  during  the  process  of 
charging.  Not  all  of  the  electrical  energy  used  in  charg- 
ing the  cell  is  converted  into  chemical  energy :  part  of  it 
goes  into  heat,  which  is  dissipated.  It  is  well  to  remem- 
ber, therefore,  that  it  takes  longer  to  charge  a  storage  cell 
than  it  does  to  discharge  it,  the  rate  of  current  flow  being 
the  same  in  both  cases.  This  limits  the  full  use  of  a  given 
cell  or  set  of  cells  to  less  than  twelve  hours  out  of  twenty- 
four. 


EL  E  CTROT  YPING 


445 


FIG.   138.  —  SILVER  PLATING. 


414.  Electroplating,    or    the    electrical    deposition    of    a 
coating  of  an  expensive  metal  on  a  cheaper  one,  is  one  of 
the  most  important  applications  of  electrolysis  (Fig.  138). 
The  process  of  copper  plating  may  be  taken  as  a  typical 
example.      The  anode  is  a  plate 

of  copper,  the  cathode  is  the 
article  to  be  plated,  and  the 
electrolyte  a  solution  of  some 
copper  salt,  as  copper  sulphate. 
When  current  is  supplied  to  the 
electroplating  cell,  the  Cu++ions 
in  the  solution  travel  toward  the 
cathode,  lose  their  charges,  and 
the  metallic  copper  is  deposited 
on  the  cathode,  as  was  explained 

in  connection  with  the  Daniell  cell  (§  411).  At 
the  anode,  fresh  Cu++  ions  are  constantly  entering  the 
solution  to  take  the  place  of  those  deposited  on  the  plated 
article.  Thus  a  solution  of  constant  concentration  is  main- 
tained. The  rate  at  which  the  current  passes  must  be 
carefully  regulated,  as  upon  this  depends  the  fineness  of 
the  deposit  and  its  adherence  to  the  object  being  plated. 
For  gold  or  silver  plating,  gold  or  silver  anodes  (Fig.  138,  a) 
are  used,  and  the  electrolyte  (5)  is  gold  or  silver  cyanide, 
as  the  case  may  be.  Plated  tableware  is  made  in  this 
way.  Other  metals  may  be  plated  with  brass,  by  employ- 
ing a  brass  anode  and  a  solution  containing  a  mixture  of 
copper  and  zinc  salts  in  the  proper  proportion. 

415.  Electrotyping.  —  Any- object  may  be  electroplated  if 
it  is  first  given  a  conducting  surface.     This  fact  is  utilized 
in  preparing  the  plates  from   which  books   are   printed. 
Lead  type  would  quickly  become  dull  if  used  to  print 
thousands  of  copies.     So  an  impression  of  the  type  of  the 


446  ELECTROCHEMISTRY 

page  is  made  in  wax  and  the  surface  coated  with  finely 
powdered  graphite.  This  coated  wax  surface  is  then 
made  the  cathode  of  a  copper  plating  bath  and  a  current  is 
sent  through  the  bath,  until  a  plating  is  obtained  which 
is  thick  enough  to  retain  its  shape  when  removed. 
The  wax  is  carefully  melted  away,  leaving  a  thin  sheet  of 
copper,  which  is  exactly  like  the  original  page  of  type. 
Melted  lead  or  other  easily  fusible  metal  is  poured  into  the 
back  of  the  copper  plate  to  give  it  strength,  and  the  electro- 
type, as  it  is  called,  is  mounted  on  a  wooden  block  and  is 
ready  for  use  in  the  press.  The  entire  process  just  de- 
scribed is  called  electrotyping.  The  electrotype  plates 
may  be  used  for  thousands  of  impressions,  and  the  type 
originally  used  for  making  them  may  be  utilized  again  for 
other  pages. 

As  every  detail  of  the  mold  is  reproduced  in  a  properly 
made  electrotype,  this  process  makes  possible  the  reproduc- 
tion in  metal  of  any  object  of  suitable  size.  A  careful 
mold  of  the  object  is  made  and  electrotyped,  and  then  the 
electrotype  is  filled  with  some  suitable  material  to  give  it 
strength.  Metal-coated  clay  statuettes  and  "silver  de- 
posit "  glass  vases  are  made  by  an  electroplating  process 
similar  to  electrotyping,  in  that  the  object  is  first  given  a 
conducting  coating  and  then  electroplated. 

416.  Refining  of  Metals.  —  Another  important  application 
of  the  electroplating  process  is  in  the  refining  of  metals. 
The  salts  of  different  metals  require  different  electromo- 
tive forces  for  their  electrolysis.  If,  for  example,  the 
anode  of  a  copper  plating  bath  consists  of  an  alloy  of  cop- 
per with  other  metals,  the  electromotive  force  applied  to 
the  bath  may  be  so  adjusted  that  only  the  copper  will  be 
transferred  by  the  current  to  the  cathode,  while  the  other 
metals  fall  to  the  bottom  of  the  cell.  This  process  is  ac- 


REFINING   OF  METALS 


447 


tually  employed  as  the  final  step  in  the  refining  of  copper 
(Fig.  139).  After  the  copper  has  been  refined  as  far  as 
possible  by  other  processes,  it  is  cast  into  plates.  These 
are  then  made  the  anodes  in  a  copper  sulphate  bath,  the 
cathodes  being  pure  copper.  As  the  current  passes,  elec- 
trolytic copper  of  nearly  100  %  purity  is  deposited  on  the 
cathode  plates.  Sometimes  pure  cathode  plates  are  not 
used,  but  the  impure  plates  are  so  arranged  that  copper  from 
the  front  of  one  plate  is  deposited  on  the  back  of  the  next. 


.I  •  .1.1. 


till  I 


£a* 


By  courtesy  of  The  Scientific  American. 

FIG.   139.  —  TANK  HOUSE  FOR  ELECTROLYTIC  COPPER  REFINING. 

The  same  principle  is  applied  to  the  separation  of  gold 
and  silver  from  each  other.  The  alloy  is  made  the  anode 
pla'te  in  a  solution  of  silver  nitrate.  The  cathode  is  a  sil- 
ver plate,  and  the  electromotive  force  is  so  adjusted  that 
only  the  silver  is  deposited.  To  retain  the  gold  as  the 
anode  plate  disintegrates,  the  anode  is  surrounded  with  a 
canvas  bag. 


448  ELECTROCHEMISTRY  .          .     • 

417.  Gold  and  Silver  Plating.  — When  silver  salts  are 
electrolyzed,  the  silver  forms  a  crystalline  coating  on  the 
cathode.  The  granular  structure  of  such  a  coating  makes 
it  unsuitable  for  use  in  silver  plating.  If,  however,  a 
solution  containing  a  mixture  of  potassium  silver  cyanide 
and  potassium  cyanide  is  used  as  an  electrolyte,  a  coherent 
layer  of  silver  is  deposited  on  the  cathode.  Such  a  solu- 
tion is,  consequently,  suitable  for  silver  plating. 

The  changes  which  take  place  during  this  process  of 
plating  with  silver  are  much  more  complex  than  those  men- 
tioned in  the  case  of  copper  plating.  Potassium  silver 
cyanide,  when  dissolved  in  water,  dissociates  according  to 
the  equation : 

KAg(CN),         5±        K+        +     Ag(CN)2- 

potassium  silver  cyanide  potassium  ion         silver  cyanide  ion 

molecule 

On  the  passage  of  the  current,  the  potassium  liberated  at 
the  cathode  immediately  reacts  with  the  potassium  silver 
cyanide  in  the  solution  replacing  the  silver,  which  is  de- 
posited at  the  cathode : 

KAg(CN)2        +       K      — >-       2KCN       +  Ag 

potassium  silver  cyanide        potassium  potassium  cyanide        silver 

At  the  anode  the  Ag(CN)2~  ions,  on  losing  their  charge, 
dissolve  silver  sufficient  to  form  silver  cyanide : 

Ag(CN)2      +      Ag      — v      2AgCN 

silver  cyanide  radical  silver  silver  cyanide  molecules 

The  silver  cyanide  unites  with  the  free  potassium  cyanide 
in  the  solution  and  potassium  silver  cyanide  is  formed. 
To  obtain  good  results,  it  is  necessary  to  stir  the  bath 
during  the  operation  of  plating. 

When  potassium  gold  cyanide  and  potassium  copper 
cyanide  are  used  in  electrolytic  baths,  changes  similar  to 


SUMMARY  449 

those  just  described  take  place.     The  best  deposits  of  cop- 
per on  iron  are  obtained  by  the  cyanide  process. 


SUMMARY 

Electrolytes  are  solutions  in  which  the  dissolved  substance  dis- 
sociates into  positively  and  negatively  charged  ions, "on  dissolving. 
The  passage  of  a  current  through  an  electrolyte  is  accompanied 
by  the  liberation  of  hydrogen  or  a  metal  at  the  cathode  (—  elec- 
trode), and  a  non-metal  or  non-metallic  radical  at  the  anode 
(+  electrode). 

Non-Electrolytes  are  solutions  in  which  no  dissociation  takes 
place  on  dissolving. 

Electrolysis  is  the  permanent  decomposition  of  an  electrolyte 
by  the  passage  of  a  current  through  it.  When  ions  lose  their 
charge  at  the  electrodes,  they  may  react  with  the  water  or  with 
the  electrodes,  as  they  then  become  simply  atoms  or  groups  of 
atoms. 

An  Acid,  on  dissolving,  yields  positive  hydrogen  ions.  A  Base, 
on  dissolving,  yields  negative  hydroxyl  ions. 

Neutralization  consists  in  the  union  of  the  hydrogen  ions  from 
the  acid  with  the  hydroxyl  ions  from  the  base  to  form  undissociated 
water.  When  the  solution  containing  the  remaining  ions  is  evap- 
orated, the  residue  is  a  salt. 

A  Precipitate  will  be  formed  when  two  electrolytes  are  mixed, 
provided  the  positive  ions  of  one  electrolyte  can  unite  with  the 
negative  ions  of  the  other  to  form  an  insoluble  compound. 

A  Simple  Voltaic  Cell  consists  of  a  zinc  plate  and  a  copper  plate 
immersed  in  dilute  sulphuric  acid.  It  converts  chemical  energy 
into  electrical  energy. 

The  Polarization  of  a  cell  is  due  to  the  collection  of  hydrogen 
bubbles  at  the  cathode.  A  Depolarizer  is  a  substance  used  to 
prevent  this  action. 


450  ELECTROCHEMISTR  Y 

The  Daniell  Cell  has  its  copper  plate  immersed  in  copper  sul- 
phate solution  to  prevent  polarization. 

The  Leclanche*  Cell  has  carbon  and  zinc  electrodes ;  the  elec- 
trolyte is  ammonium  chloride  and  the  depolarizer  is  manganese 
dioxide.  The  Dry  Cell  is  a  modification  of  the  Leclanche  cell. 

The  Lead  Storage  Cell  has  electrodes  of  lead  and  lead  peroxide. 
The  electrolyte  is  dilute  sulphuric  acid.  In  discharging,  both  plates 
become  covered  with  lead  sulphate.  They  are  restored  to  their 
original  condition  by  passing  a  current  through  the  cell  (charging). 

The  Edison  Storage  Cell  uses  nickel  peroxide  and  iron,  with 
caustic  soda^s  the  electrolyte. 

Objects  are  Electroplated  by  making  them  cathodes  in  an  elec- 
trolytic bath,  of  which  the  anode  is  composed  of  the  plating  metal 
and  the  electrolyte  is  a  salt  of  that  metal. 

In  Electrotyping,  a  mold  of  the  object  to  be  copied  is  covered 
with  graphite  and  plated  with  a  shell  of  copper  thick  enough  to 
retain  its  form  when  detached. 

Some  Metals  are  Refined  by  making  them  anodes  in  an  electro- 
lytic bath,  with  a  cathode  made  of  the  cure  metal  and  a  salt  of 
the  metal  as  the  electrolyte. 

EXERCISES 

1.  How  does  the  conduction  of  an  electric  current  through 
a  copper  wire  differ  from  that  through  salt  wate^r  ? 

2.  Explain   clearly  the  meaning   of   the   following  terms : 
anode ;  cathode ;  ion  ;  electrolyte ;  depolarizer. 

3.  State,  with' equations,  what  takes  place  when  : 

(a)  a  few  drops  of  nitric  acid  are  poured  into  a  beaker 
of  water ; 

(6)  a  few  pieces  of  caustic  potash  are  dropped  into  an- 
other beaker  of  water ; 

(c)   the  contents  of  the  two  beakers  are  mixed. 

4.  Write  the   symbols  of   the   ions  formed,  indicating  the 
proper  number  of  charges,  when  the  following  compounds  are 


EXERCISES  451 

dissolved  in  water :  Cu(N08)2;  HBr;  Na2C03;  ZnS04;  NH4OH ; 
NaHS04. 

5.  Barium  choride  (BaCl2)  is  soluble  in  water.     Barium 
sulphate  (BaS04)  is  insoluble.     Devise  a  test  for  the  S04+  ion 
based  on  these  facts. 

6.  Describe  two  litmus  tests,  stating  for  what  ion  each  test 
is  used. 

7.  Make  a  sketch  of  the  apparatus  for  the  electrolysis  of  a 
solution  of  sulphuric  acid.     Describe  and  explain  the  action. 

8.  Make  a  comparative  table  of  the  simple,  Daniell,  and 
Leclanche  cells  under  the  following  headings :  Name ;  positive 
plate ;   negative  plate  ;  electrolyte  ;  depolarizer  ;  chemical   re- 
action. 

9.  Explain  the  depolarization  of  the  Daniell  and  of  the  Le- 
clanche cell. 

10.  Lead  sulphate  is  a  non-conductor  of  electricity.     What 
would  be  the  effect  on  a  storage  cell  of  continuing  the  discharge 
until  the  plates  were  entirely  covered  with  lead  sulphate  ? 

11.  Explain  the  advantage  of  an  Edison  storage  cell,  as 
compared  with  a  Daniell  cell. 

12.  Make  a  diagram  of  a  copper  plating  cell,  marking  the 
electrodes  and  indicating  the  direction  of  the  current. 

13.  Describe  an  electrical  method  of  separating  the  silver 
of  a  piece  of  sterling  silver  (§  183)  from  the  metal  alloyed 
with  it. 

14.  What  is  electrolytic  copper  ?     How  is  it  produced  ? 

15.  State  what  would  happen  during  the  passage  of  a  cur- 
rent through  a  solution  of  sodium  sulphate. 

16.  Could  metallic  sodium  be  produced  by  the  electrolysis 
of  a  water  solution  of  one  of  its  salts  ?     Explain. 

17.  How  could  you  give  a  plaster  cast  a  surface  layer  of 
copper*? 

18.  How  would  you  gold  plate  the  inside  of  a  silvet  cup  ? 


CHAPTER   XXXVIII 

CORROSION  OP  METALS 

NATURE   OF   CORROSION 

418.  Surface  Change  on  Metals.  —  When  freed  from  sur- 
face  deposit    by  polishing,  all  metals  present   a   highly 
lustrous  appearance  .which    is    so    characteristic    that   it 
is  spoken  of  as  " metallic  luster."     In  the  case  of  most 
metals,  owing  to  chemical  action  by  constituents  of  the 
air,  this  surface  remains  unchanged  for  only  a  short  time. 
The  quickness  of  the  change  is  most  noticeable  with  very 
active  metals  like  sodium  and  potassium,  in  which  cases 
the  luster  lasts  but  a  few  seconds.     Less   active  metals 
change  more  slowly  and  the  very  inactive  ones  like  gold 
and  platinum  do  not  change  even  after  long  periods  of 
time.     Between  the  two  extremes  lie  the  common  metals, 
iron,  zinc,  lead,  copper,  which  corrode  easily,  and  silver, 
nickel,  and  aluminum,  which  are  less  subject  to  change. 

419.  Constituents  of  the  Air  Active  in  Causing  Corrosion. — 
Oxygen  is  ordinarily  regarded  as  the  substance  in  the  air 
responsible  for  the  change,  for  the  reason  that  the  cor- 
roded matter  is  largely  composed  of  oxide  of  the  metal. 
It  is  probably  true,  however,  that  oxygen  is  not  the  sole 
cause  of  the  action  in  the  majority  of  cases.     Moisture, 
carbon  dioxide,  and,  in  the  vicinity  of  cities  or  large  man- 
ufacturing  plants,    gaseous    sulphur   compounds    formed 
from  burning  coal  and  gas,  play  an  important  part  in  the 
corrosion. 

452 


NATURE   OF  CORROSION  453 

Considering  first  the  case  of  iron,  the  most  useful  and, 
unfortunately,  the  most  easily  corroded  of  all  common 
metals,  experiments  show  that  : 

(1)  iron  does  not  rust  in  pure  dry  oxygen, 

(2)  iron  does  not  rust  in  the  presence  of  air  and  water 
if  carbon  dioxide  is  absolutely  removed  (except  when  the 
temperature  is  above  22°  C.  and  the  same  water  remains 
in  contact  with  the  iron  for  some  time), 

(3)  acid  vapors  hasten  the  corrosion  of  iron,  and 

(4)  bases  retard  the  corrosion. 

These  observations  make  probable  the  conclusion  that 
under  ordinary  conditions  the  corrosion  of  iron  is  started 
by  the  combined  action  of  carbon  dioxide  and  water,  that 
is,  by  carbonic  acid  : 

H20   +   C02— >-H2C03 

water         carbon  carbonic 

dioxide  acid 

The  products  of  this  first  action  are  ferrous  carbonate, 
FeCOg,  and  hydrogen  : 

Fe  +  H2CO3  — >-   FeCOg     +        H2 

iron         carbonic  ferrous  hydrogen 

acid  carbonate 

All  ferrous  compounds  will  change  into  ferric  compounds 
if  they  are  in  contact  with  air  (oxygen)  and  water.  The 
substance  formed  will  be  ferric  hydroxide,  Fe(OH)3,  if  no 
free  acid  is  present.  Hence  the  initial  corroding  action 
is  immediately  followed  by  one  represented  in  the  follow- 
ing equation : 

4  FeC03  +  6  H20  +  O2  — •»-  4  Fe(OH)8  +  4  CO2 

ferrous  water       oxygen  ferric  carbon 

carbonate  hydroxide  dioxide 

The  carbon  dioxide  which  started  the  action  is  thus  again 
set  free  and  begins  anew  the  initial  action.  The  ferric 


454  CORROSION  OF  METALS 

hydroxide  does  not  remain  unchanged,  but,  by  loss  of 
water,  is  partly  converted  into  the  oxide,  Fe2O3 : 

2  Fe(OH)8  -^  Fe203  +  3  H2O 

ferric  ferric  water 

hydroxide  oxide 

All  these  conclusions  agree  with  an  additional  experimen- 
tal observation,  that  iron  rust  is  composed  of  ferric  oxide, 
some  unchanged  ferric  hydroxide,  and  traces  of  ferrous 
carbonate. 

420.  Corrosion  of  Other  Metals.  —  The  corrosion  of  other 
common  metals  is  a  far  less  serious  matter  than  that  of 
iron.     In  so  far,  however,  as  it  does  occur,  it  is  also  true 
that  oxygen  is  probably  not  the  sole  cause  of  the  change. 
In  the  case  of  silver,  the  corroded  matter  is  largely  sul- 
phide, caused  by  the  action  of  gaseous  sulphur  compounds 
of  the  air  ;    the  coating  formed  on   copper   may  include 
copper  sulphide,  cuprous  oxide,  cupric   oxide,  and  basic 
carbonate  of  copper.     The  last  named  of  these  substances 
is  the  one  which  gives  to  exposed  copper  the  beautiful 
green  color  that  it  sometimes  shows.     On  lead  we  find  an 
analogous  mixture  of  compounds,  and 'such   is   the   case 
with  zinc.     In  all  these  cases  the  composition  of  the  sur- 
face deposit  will  vary  with  the  conditions. 

PREVENTION   OF   CORROSION 

421.  Self-Protective  Metals. — In  a  sense,  all  the  common 
metals  except  iron  are  self-protective  against    corrosion. 
This  is  true  because  the  deposit,  when  once  formed,  acts 
like  a  paint  and  prevents  action  by  atmospheric  agents. 
Lead  used  on  the  roofs  of  cathedrals  built  in  the  Middle 
Ages,    on   being   scratched,   shows   only   a   thin    surface 
deposit  with  the  bright  metal  underneath.     Copper  rain- 
spouts   and  cornice  work  of   buildings  are   usually   not 


PREVENTION  OF  CORROSION  455 

painted,  but  are  allowed  to  form  their  own  protective 
coatings  by  corrosion.  In  the  case  of  zinc,  t>he  corrosion 
proceeds  somewhat  more  rapidly.  Tin,  nickel,  and 
aluminum  remain  almost  free  from  action,  except  that 
aluminum  used  for  electric  transmission  lines  shows  a 
coating  that  is  not  well  understood. 

422.   Iron  Bust  a  Catalytic  Agent  for  its  Own  Production.  — 

As  is  well  known,  the  rusting  of  iron  proceeds  very  rapidly 
where  it  has  once  started.  To 
preserve  metal  where  this  has 
happened  is  a  very  difficult  mat- 
ter, and  is  scarcely  possible  by 
any  means,  without  first  re- 
moving the  existing  deposit. 
It  appears,  therefore,  that  iron 
rust  is  a  catalytic  agent  for  the 
production  of  iron  rust.  The 
explanation  of  this  fact  is  not 
definitely  known,  but  one  be- 
lief is  that  an  electrolytic  ac- 
tion is  set  up  like  that  which 
occurs  in  batteries.  The  rust 
of  iron  acts  as  a  cathode  of  the 

cell,  the  unchanged  iron  as  an 

..  ,         ii..-,  -,    FIG.  140.  —  CORROSION  OF  IRON. 

anode,  and  carbon  dioxide  and 

water,  together  forming  carbonic  acid,  make  the  active 
solution.  Currents  of  electricity  circulate  through  the 
particles  of  rust,  particles  of  unchanged  metal,  and  the 
solution,  with  the  result  that  iron,  like  the  zinc  of 
the  cell,  is  dissolved,  and  ferric  oxide  and  ferric  hy- 
droxide are  eventually  formed.  In  this  way  it  is  possible 
for  the  iron  to  be  rusted  through  and  through  in  a  com- 
paratively short  space  of  time. 


456  CORROSION   OF  METALS 

This  fact  makes  a  great  deal  of  trouble  in  using  the 
metal,  and  makes  the  permanency  of  iron  structures  a 
doubtful  matter.  It  is  practically  always  necessary  to 
protect  the  metal  with  some  coating.  Unfortunately,  no 
thoroughly  satisfactory  substance  for  this  purpose  has 
been  discovered. 

423.  Protecting  Iron  by  Deposits  of  Other  Metals.  —  Iron 
can  be  protected  reasonably  well  by  covering  it  with  a 
thin  layer  of  another  metal  which  is  either  free  from  cor- 
rosion, or  self-protective  against  corrosion.  One  method 
of  accomplishing  this  result  is  to  dip  the  thoroughly 
cleaned  iron  into  the  melted  metal.  Either  tin  or  zinc  is 
used  for  the  purpose.  Tin  does  not  protect  against  cor- 
rosion nearly  so  well  as  zinc,  but,  since  this  latter  metal 
readily  forms  poisonous  compounds,  tin  must  be  applied 
where  the  article  is  to  serve  as  a  food  container  or  cooking 
utensil.  Zinc  does  much  better  where  the  iron  is  used  in 
making  pails  or  troughs,  or  where  it  is  to  be  used  for 
building  purposes.  Iron  that  has  been  covered  with  tin 
is  spoken  of  as  "  tin  ware  "  ;  that  which  has  been  covered 
with  zinc  is  called  "  galvanized  "  iron. 

Another  method  of  applying  a  coating  of  one  metal  to 
another  is  found  in  the  use  of  the  electric  current  as  ex- 
plained in  §  414.  By  means  of  electrolysis,  nickel  is  de- 
posited on  an  iron  object  by  making  it  the  cathode  in  an 
electrolytic  cell  containing  a  solution  of  nickel  ammonium 
sulphate.  When  definite  conditions  are  established,  a  very 
good  protective  coating  is  secured  if  the  iron  has  first  been 
covered  in  a  similar  manner  with  a  thin  coating  of  copper. 
Since  nickel  has  a  pleasing  color  and  takes  a  high  polish, 
nickel  plating  is  especially  desirable  for  an  ornamental 
finish. 

An  electrolytically  deposited  coating  is  very  uniform  in 


CEMENT  AS  A   PROTECTIVE   COATING         457 

thickness  and  can  be  made  extremely  thin.  Hence,  the 
method  is  much  used  as  a  means  of  coating  cheap  metal 
with  an  expensive  one,  as  in  making  "  plated "  forks, 
spoons,  and  knives  for  table  use,  and  in  the  manufacture 
of  cheap  jewelry. 

424.  Protection  by  Paints.  —  When  large  surfaces  of  iron 
are  to  be  covered,  paints  are  usually  employed  as  protec- 
tive agents.     This  method  is  seldom  completely  successful, 
and  the  coating  of  paint  has  to  be  renewed  frequently. 
This  is  largely  because  the  iron  is  not  entirely  free  from 
initial  rust  when  the  paint  is  first  applied.     This  rust  in- 
duces catalytically  further  rusting  underneath  the  paint, 
which  consequently  flakes  off.     The  usefulness  of  a  paint 
coating  depends  on  the  nature  of  the  paint  base  that  is 
mixed  with  linseed  oil  in  making  the  paint,  and  also  on 
minor  impurities  which  are  present.     Red  lead,  Pb3O4,  is 
usually  regarded  as  the  best  substance  for  this  purpose. 
Iron  oxide,  Fe2O3,  is  cheaper  and  is  much  used,  but  it  is 
not  so  effective.     Asphaltum  is  applied  to  the  iron  used 
for    boilers    and    sometimes    for    machinery.      Powdered 
aluminum    and,   less    often,    powdered   copper    are   used 
where  a  metallic  finish  is  desired. 

425.  Cement  as  a  Protective  Coating.  —  In  recent  years,  it 
has  been  a  common  practice  to  cover  the  steel  framework 
of  large  buildings  with  a  coating  of  cement  to  prevent 
corrosion.     It  acts  practically  as  a  paint.     The  thickness 
of  the  layer  used  varies  from  a  brush  coating  to  one  of 
from  one  to  three  inches  in  depth.     Experiments  have 
indicated  that  this  gives  a  method  of  greatly  retarding 
the  rusting.     But  we  cannot  be  certain  that  it  gives  a 
permanent  protection,  for  the  reason  that  not  enough  time 
has  passed  to  enable  us  to  judge.     Cement  is  superior  to 


458  CORROSION  OF  METALS 

paint  in  that  it  does  not  easily  flake  off.  Furthermore, 
since  cement  is  alkaline,  it  tends  to  prevent  rusting,  as 
we  have  seen  that  iron  does  not  corrode  readily  in  the 
presence  of  alkalies.  But  cement  is  porous,  and  water 
and  the  gases  of  the  air  will  diffuse  through  it.  Hence 
it  is  quite  possible  that  rusting  may  occur  slowly  under- 
neath the  cement. 

426.   The  Magnetic  Oxide  of  Iron  as  a  Protective  Coating  - 

The  magnetic  oxide  of  iron,  Fe3O4,  makes  a  very  effective 
protective  coating  for  iron  if  it  is  deposited  on  the  surface 
of  the  metal  in  a  firmly  adhering  layer.  This  oxide  is 
very  different  from  ferric  oxide,  Fe2O3,  since  it  has  no 
catalytic  effect  in  inducing  oxidation.  The  process  con- 
sists in  subjecting  the  hot  iron  or  steel  to  the  action  of  a 
mixture  of  superheated  steam  and  carbon  dioxide.  The 
carbon  dioxide  prevents  the  formation  of  any  ferric  oxide. 
The  equation  is : 

3  Fe   +  4  H2O  — »-    Fe3O4    +      4  H2 

iron  water  magnetic  hydrogen 

iron  oxide  > 

This  affords  what  is  probably  the  best  protective  coating 
for  iron  and  steel.  Spots  of  rust  do  not  readily  spread  if 
they  form  where  the  coating  has  by  chance  worn  off. 
The  process  has  the  disadvantage  that  it  cannot  be  applied 
to  metal  that  has  been  put  in  place  in  structural  work. 
Each  piece  must  be  separately  treated  at  the  factory,  and 
it  cannot  be  hammered  or  riveted  into  place,  as  this  treat- 
ment would  break  the  coating,  and  give  rise  to  local 
rusting. 

Russia  iron  is  iron  covered  with  a  coating  of  magnetic 
oxide.  It  is  used  for  stove  pipes,  the  covering  for  loco- 
motive boilers,  and  similar  purposes. 


EXERCISES  459 

SUMMARY 

Various  Constituents  of  the  Air  act  with  greater  or  less  rapidity 
on  metals.  This  action  does  not  seriously  affect  most  metals, 
except  in  appearance,  because  the  action  stops  after  a  thin  layer 
of  corroded  matter  has  been  formed. 

The  Corrosion  of  Iron,  however,  is  a  very  serious  matter,  since 
the  rust,  when  once  formed,  acts  as  a  catalytic  agent  for  the  for- 
mation of  more  rust.  Consequently  the  metal  may  rust  through 
in  a  comparatively  short  time.  Iron  rust  consists  of  a  mixture 
of  ferric  oxide,  ferric  hydroxide,  and  ferrous  carbonate. 

Iron  does  not  Rust  in  the  presence  of  bases,  but  corrodes  very 
rapidly  in  the  presence  of  acid  fumes.  A  commonly  accepted 
theory  of  its  corrosion  is  based  on  the  fact  that  carbon  dioxide  and 
water  form  a  weak  acid,  carbonic  acid.  The  theory  is  that  the 
rusting  starts  with  the  action  of  this  acid,  and  that  ferrous  car- 
bonate, FeCO3,  is  formed  ;  that  this  substance  is  next  changed 
by  moisture  and  oxygen  of  the  air  into  ferric  hydroxide,  Fe(OH)3, 
with  the  liberation  of  carbon  dioxide.  This  liberation  of  carbon 
dioxide  "  on  the  spot  "  explains  why  rusting  proceeds  very  rap- 
idly where  it  has  once  started.  The  ferric  hydroxide  is  partly 
decomposed  into  ferric  oxide,  Fe203,  and  water. 

Iron  is  protected  against  Corrosion  by  these  methods  :  (a)  paint- 
ing, which  is  not  very  effective,  and  which  must  be  done  repeatedly  ; 
(b)  coating  with  cement,  which  is  more  successful,  but  not 
necessarily  wholly  effective  ;  (c)  coating  with  magnetic  oxide, 
Fe304,  by  the  action  of  steam  at  a  high  temperature  ;  (d)  dip- 
ping the  iron  into  melted  tin  (tin  plate)  or  melted  zinc  (galvanized 
iron)  ;  (e)  electroplating  with  either  zinc,  copper,  or  nickel. 

EXERCISES 

1.  What  connection  is  there  between  the  chemical  activity 
of  a  metal  and  the  ease  of  its  corrosion  ?  Name  two  active 
metals ;  two  moderately  active  metals ;  two  inactive  metals. 


460  CORROSION  OF   METALS 

2.  What  constituents  of  the  air  cause  the  corrosion  of  iron  ? 
Of  silver  ?     Of  copper  ? 

3.  Explain  why  iron  tools  rust  much  more  rapidly  in  a  chem- 
ical laboratory  than  elsewhere. 

4.  State  a  theory  that  explains  the  rusting  of  iron  by  the 
constituents  of  the  air. 

5.  Why  do  surgeons,  in  sterilizing  their  instruments,  boil 
them  in  a  solution  that  contains  a  little  alkali  ? 

6.  Which  substance  makes  the  best  material  for  roofing  or 
cornice  work  :  tin  plate,  galvanized  iron,  or  copper  ?     Why  ? 

7.  Why  was  lead  so  frequently  used  as  a  roofing  material 
for  castles  and  cathedrals  during  the  Middle  Ages  ? 

8.  What  is  meant  by  saying  that  "  iron  rust  is  a  catalytic 
agent  for  its  own  formation  "  ? 

9.  Why   are  tools,  when  bought  at  a  hardware  store,  fre- 
quently found  to  be  covered  with  grease  ? 

10.  What  is  tin  plate  ?     How  is  it  made  ?     What  is  gal- 
vanized iron  ?     How  is  it  made  ? 

11.  In  what  ways  is  a  covering  of  nickel  superior  to  one  of 
tin  or  zinc?- 

12.  Why  are  iron  kitchen  utensils  and  dishes  usually  cov- 
ered with  tin  in  preference  to  other  metals  ? 

13.  What  precautions  should  be  taken  before  applying  paint 
to   iron   structures  ?     Why   is  it   necessary   to   repaint  such 
structures  frequently  ? 

14.  What  advantages  has  concrete  as  a  protective  coating 
for  iron  ? 

15.  Concrete  that  contains  iron  or  steel  reenforcing  rods  is 
occasionally  found  to  be  burst  open  from  within.     How  would 
you  explain  this  ? 

16.  What  is  Russia  iron  ?     How  is  it  made  ?    What  are  its 
advantages  ?     What  are  its  disadvantages  ? 

17.  The  tin  covering  on  tin  plate  usually  has  small. pin  holes* 
Why  is  this  a  serious  disadvantage  ? 


CHAPTER   XXXIX 
CLEANING  OP  METALS 

0 

427.  Polishing  and  Polishing  Powders.  —  As  we  have  seen, 
metallic  objects  which  are  not  thoroughly  covered  with 
protective  coatings  become  corroded  or  tarnished  by  the 
action  of  various  constituents  of  air  and  water.  Even 
without  a  protective  coating,  this  tarnishing  is  largely 
prevented  if  the  articles  are  in  constant  use  so  that  the 
tarnish  is  worn  off  as  fast  as  it  forms.  For  example,  the 
tools  that  a  workman  is  using  all  the  time  do  not  rust, 
while  those  of  only  occasional  use  should  be  wiped  after 
use  with  an  oily  cloth  to  keep  them  bright.  Coatings 
of  rust  or  tarnish  may  be  removed  by  abrasion,  that  is, 
polishing  with  a  material  harder  than  the  coating.  In 
such  a  process  the  fine,  gritty  particles  of  the  abrasive 
scratch  off  the  rust,  and,  if  they  are  hard  enough,  finally 
scratch  the  metal  also. 

The  two  essentials  of  a  good  polishing  powder  are  : 
(a)    it  must  be  harder  than  the  layer  of  corroded  matter, 
(7>)    its  particles  must  be  so  fine  that  they  will  not  make 
noticeable  scratches  on  the  surface  of  the  metal. 

A  very  hard  abrasive  should  not  be  used  on  a  soft  metal, 
as  it  will  remove  too  much  of  the  metal  itself  with  the 
corroded  layer. 

A  deposit  known  as  infusorial  earth  (Fig.  141)  is  found 
in  many  localities.  This  mainly  consists  of  glassy  skele- 
tons of  microscopic  plants,  arid  is  chiefly  silicon  dioxide, 
SiO2.  It  is  nearly  as  hard  as  sand  or  ground  quartz, 
which  is  also  silicon  dioxide.  This  infusorial  earth  makes 

461 


462 


CLEANING   OF  METALS 


FIG.    141.  —  INFUSORIAL   EARTH,   HIGHLY 
MAGNIFIED. 


a  most  desirable  polishing  powder  for  metals,  as  it  com- 
bines hardness,  which  makes  its  action  rapid,  with  ex- 
ceeding fineness  of  grain, 
which  keeps  it  from 
scratching.  It  is  a  very 
common  ingredient  of 
polishing  powders, 
pastes,  and  soaps.  Diato- 
maceous  earth,  tripoli, 
and  electro-silicon  are 
other  names  of  this  ma- 
terial. 

Powdered  silica  has 
largely  replaced  infuso- 
rial earth  for  all  pur- 
poses except  the  finest 
polishing,  because  it  is 
much  cheaper  and  purer.  It  is  made  by  crushing  quartz, 
sandstone,  or  other  silica  rock  to  a  fine  powder  with  stamp 
mills,  and  grading  the-  powder  according  to  fineness  for 
the  different  uses  to  which  it  is  to  be  put.  It  is  the  polish- 
ing material  contained  in  scouring  soaps  and  most  polish- 
ing powders.  As  powdered  silica  is  alwa}^s  coarser  grained 
than  infusorial  earth,  soaps  and  powders  containing  it 
should  not  be  used  on  finely  burnished  surfaces,  such  as 
gold  and  silver.  Ground  sandstone  is  often  made  into 
scouring  bricks,  known  as  Bath  or  Bristol  Bricks. 

Another  polishing  material  of  similar  chemical  nature 
is  pumice.  This  is  a  mixture  of  silicates  ejected  from 
volcanoes  as  lava.  Pumice,  even  ground  to  a  fine  powder, 
is  coarser  grained  than  powdered  silica,  and  so  it  is  more 
likely  to  scratch  the  surface.  For  coarse  polishing, 
powdered  pumice  and  water  are  used,  then  the  rough 
surface  is  further  smoothed  with  fine  pumice  and  oil. 


FERRIC    OXIDE  463 

Finally,  infusorial  earth  is  used,  as  its  scratches  are  too 
small  to  mar  the  surface.  Great  aare  must  be  taken  in 
the  final  polishing  of  any  article  to  avoid  the  presence  of 
a  single  coarse  grain,  as  that  would  leave  a  visible  scratch 
each  time  it  was  rubbed  over  the  surface. 

428.  Ferric  Oxide,  Fe2O3,  is  extensively  -used  for  fine 
polishing  under  the  names  of  rouge,  colcothar,  crocus,  and 
jeweler's  red.  Both  naturally  occurring  and  artificially 
prepared  ferric  oxide  are  used.  In  either  case  the  material 
must  be  ground  very  fine,  carefully  washed,  and  freed  from 
coarse  or  gritty  grains.  Rouge  is  used  dry  or  mixed  with 
water,  alcohol,  or  grease,  according  to  the  nature  of  the 
work.  The  red  polishing  pastes  or  "  Putz  pomades  "  so 
commonly  used  consist  chiefly  of  rouge  and  grease.  They 
are  excellent  for  cleaning  all  metals  except  silver  and 
gold.  Jewelers  use  fine-grained  rouge  for  the  latter 
metals,  but  for  household  use  fine  infusorial  earth  prepara- 
tions, like  electro-silicon,  are  to  be  preferred  for  the  pre- 
cious metals. 

Castings  and  forgings,  particularly  of  iron,  usually  re- 
quire a  preliminary  grinding  before  they  are  polished. 
There  are  three  materials  widely  used  for  grinding. 
Silica,  SiO2,  is  used  in  the  form  of  sand  in  the  sand  blast 
for  cleaning  castings,  and  in  the  massive  form  is  the  chief 
material  in  grindstones  and  oilstones.  The  second  mate- 
rial is  aluminum  oxide,  A12O3.  This  occurs  naturally  in 
the  mineral  corundum,  of  which  emery  is  an  impure  form  ; 
when  prepared  in  the  electric  furnace,  it  is  known  as 
alundum.  Both  forms  are  harder  than  silica  and  are 
widely  employed  in  powder  of  various  grades  of  fine- 
ness and  in  wheels.  Emery  powder  is  also  cemented  to 
cloth,  paper,  and  sticks  by  means  of  shellac  and  glue.  The 
third  and  hardest  abrasive  is  carborundum.  This  is  silicon 


464  CLEANING   OF  METALS 

carbide,  SiC,  produced  from  coke  and  sand  in  an  electric 
furnace  (§ 


SiO2       +       30       —  ^      SiC       +       2CO 

silicon  carbon  carborundum  carbon 

dioxide  monoxide 

The  hard  crystals  produced  in  the  furnace  are  crushed  and 
then  made  up  in  the  same  great  variety  of  forms  as  emery. 

429,  The  Chemical  Cleaning  of  Metals.  —  This  is  known  as 
"  pickling,"  and  consists  in  dissolving  oxides  or  other  for- 
eign matter  by  solutions  which  act  on  the  tarnish.  Iron 
is  usually  pickled  in  a  solution  containing  one  part  of  sul- 
phuric or  hydrochloric  acid  to  ten  of  water.  After  the 
surface  is  properly  brightened,  it  is  thoroughly  washed  to 
remove  all  traces  of  acid.  Brass  is  given  a  preparatory 
pickling  in  sulphuric  acid,  and  then  given  a  second  treat- 
ment in  dilute  nitric  acid  or  a  mixture  of  nitric  and  sul- 
phuric acids.  By  a  proper  selection  of  acids  and  an 
adjustment  of  the  strength  of  the  solution,  different  shades 
of  color  may  be  produced.  The  solutions  described  above 
should  be  employed  in  the  shop  and  should  not  be  used  in 
household  cleaning,  as  they  are  corrosive  to  flesh  and 
clothing. 

Oxalic  aeid  is  often  used  alone  or  mixed  with  some  of 
the  finer  abrasives  for  cleaning  brass  or  copper  ornaments. 
It  is  highly  poisonous,  and  articles  on  which  it  has  been 
used  should  be  thoroughly  washed  and  dried  afterwards. 
It  is  not  so  corrosive  as  the  acids  used  for  pickling,  but  on 
account  of  its  poisonous  character,  it  should  not  be  used 
on  anything  intended  to  hold  food. 

Another  poisonous  compound  used  in  cleaning  solutions 
by  jewelers  for  gold  and  silver  is  potassium  cyanide,  KCN. 
This  is  one  of  the  most  deadly  poisons  known  and  should 
never  be  used  in  the  household  for  any  purpose  whatever; 


HOUSEHOLD   CLEANING  465 

a  single  small  crystal  is  sufficient  to  cause  death.  It  is 
deplorable  that  many  cleaning  solutions  on  the  market 
contain  this  compound.  When  it  is  necessary  to  use  a 
cyanide  solution  in  the  arts,  rubber  gloves  should  be  worn 
and  the  hands  washed  repeatedly  after  taking  them  off. 
Enough  might  enter  the  system  through  a  scratch  to  pro- 
duce dangerous  poisoning  or  even  death.  "Its  value  for 
cleaning  metals  depends  upon  the  fact  that  gold  and  silver, 
as  well  as  their  sulphides,  react  with  it  to  produce  soluble 
double  cyanides.  A  short  immersion  removes  the  tar- 
nish, together  with  the  extreme  outer  layer  of  the  metal, 
leaving  a  bright,  clean  surface. 

430.  Household  Cleaning.  —  Some  methods  of  cleaning 
brass  arid  silver  have  been  given  in  preceding  sections. 
Another  cheap  and  efficient  cleaner  for  these  metals  is 
whiting  (finely  powdered  chalk,  CaCO3)  moistened  with 
ammonia.  There  is  no  very  satisfactory  polishing  material 
for  nickel  which  has  mice  become  tarnished.  Nickel- 
plated  articles,  therefore,  should  be  kept  free  from  dirt 
by  washing  with  soapsuds,  and  corrosive  liquids  should 
be  kept  from  them. 

Recently  a  simple  and  very  satisfactory  method  of 
cleaning  silverware  by  boiling  it  with  water  in  an  alumi- 
num dish  has  been  devised.  In  this  case,  aluminum  re- 
places the  silver  in  the  compounds  forming  the  tarnish. 
In  cleaning  plated  silver,  the  fact  that  the  plating  is  pure 
silver  and  hence  softer  than  ordinary  sterling  or  coin  silver 
should  be  kept  in  mind.  Plated  silver  should  never  be 
rubbed  hard,  even  with  abrasive  polishes  which  might  be 
suitable  for  solid  silver.  If  the  plated  ware  is  lacquered 
in  addition,  then  only  water  and  a  soft  cloth  should  be 
used.  If  the  lacquer  is  once  pierced,  the  exposed  silver 
will  begin  to  tarnish.  The  lacquer  should  then  be  entirely 


466  CLEANING   OF  METALS 

removed  and  the  piece  may  either  be  relacquered  or  be 
treated  like  other  plated  silver. 

Slight  discolorations  in  aluminum  kitchen  ware  may 
often  be  removed  by  cooking  some  acid  fruit  or  vegetable 
in  the  dish.  Aluminum  may  be  readily  cleaned  by  scour- 
ing with  Dutch  Cleanser,  Bon  Ami,  Sapolio,  or  any  other 
cleansing  powder  or  soap  containing  little  free  alkali. 
Soda  should  never  be  allowed  to  come  in  contact  with 
aluminum,  for  it  will  turn  the  aluminum  black.  This 
black  coating  or  any  other  persistent  discoloration  may 
be  removed  from  aluminum  by  scouring  with  steel  wool 
(No.  00),  moistened  with  soapsuds. 

SUMMARY 

Corroded  Metal  may  be  cleaned  either  (a)  by  rubbing  off  the 
coating  with  an  abrasive,  or  (b)  by  chemically  dissolving  it. 
Abrasives  must  be  a  little  harder  than  the  coating  to  be  removed 
and  so  fine-grained  as  not  ,to  scratch  the  metal  perceptibly. 

Finely  divided  Silica  (infusorial  earth  or  ground  quartz)  is  an 
excellent  polishing  powder.  Ground  pumice  stone  is  used  with 
water  for  coarse  polishing,  and  with  oil  for  fine  polishing. 

Rouge,  ferric  oxide,  is  used  either  dry  or  wet  with  water,  alcohol, 
or  grease  for  cleaning  all  metals  except  gold  and  silver. 

Castings  are  smoothed  with  sand,  sandstone,  aluminum  oxide, 
or  carborundum. 

Iron  is  pickled  in  dilute  sulphuric  or  hydrochloric  acid. 

Brass  is  pickled  first  in  dilute  sulphuric  acid  and  then  in  dilute 
nitric  acid. 

Oxalic  Acid  is  valuable  for  cleaning  brass  and  copper.  It  is 
poisonous. 

Potassium  Cyanide  is  used  by  jewelers  to  clean  gold  and  silver. 
It  is  exceedingly  poisonous. 


EXERCISES  467 

Silverware  may  be  cleaned  by  boiling  in  pure  water  in  an 
aluminum  dish.  Plated  silver  should  never  be  scoured  or  rubbed 
hard. 

Aluminum  may  be  cleaned  with  a  non-caustic  cleaner.  Bad 
disco.lorations  may  be  removed  by  scouring  with  soap  and  steel 
wool. 

Whiting,  moistened  with  ammonia,  is  a  cheap  and  efficient 
polishing  material  for  brass,  copper,  and  silver. 

EXERCISES 

1.  What  is  the  composition  of  the  surface  coating  to  be 
removed  from  tarnished  silver  ?  Copper  ?  Zinc  ?  Rusty  iron  ? 

2.  Why  do  the  blades  of  pocketknives  rarely  require  polish- 
ing ? 

3.  Why  is  sand  suitable  for  grinding,  but  not  for  polishing  ? 

4.  Give  in  detail  the  steps  necessary  to  convert  the  casting 
for  a  brass  ink  stand  into  the  finished  article. 

5.  Will   a   scouring  soap  completely   dissolve  in    water? 
Explain. 

6.  Give  the  composition  and  use  of  each  of  the  following : 
tripoli,  emery,  carborundum,  Putz-Pomade,  electro-silicon. 

7.  Describe  a   method  of   cleaning  silver   spoons   (a)  for 
household  use,  (b)  for  jeweler's  use.     WThy  should  the  jeweler's 
cleaner  not  be  used  in  the  house  ? 

8.  What  is  "pickling"  ?     Give  the  proper  pickle  for  iron  ; 
brass;  gold. 

9.  Why  may  carborundum  powders  of  different  degrees  of 
fineness  be  used  in  finishing  the  same  article  ? 

10.  Give  two  methods  of  cleaning  a  brass  door  knob. 

11.  Why  is  it  well  to  avoid  silver  polishes  advertised  to 
"  clean  without  labor  "  ? 

12.  Give  two  methods  of  cleaning  an  aluminum  dish  and 
state  when  each  should  be  employed. 


CHAPTER   XL 

IRON  AND  STEEL 

431.  Classification  of  Iron  and  Steel.  —  Iron  is  not  pro- 
duced commercially  in  a  pure  form,  as  copper  is,  but  al- 
ways contains  a  certain  proportion  of  carbon  and  other 
substances.     Differences  in  the  proportion  of  carbon  par- 
ticularly, and  in  the  way  in  which  the  carbon  is  physically 
and  chemically  related  to  the  iron,  give  rise  to  a  large 
number  of  metallic  substances  which   may  be  included 
under  the  general  classes,  cast  iron,  wrought  iron,  and  steel. 
The  differences  in  the  properties  of  the  finished  products 
are  due  to  the  character  of  the  original  ore,  to  substances 
added  to  or  taken  from  the  ore,  and  to  the  heat  treatment 
received  during  manufacture.     The  nature  and  composi- 
tion of  each  of  the  main  varieties  of  iron  and  steel  will  be 
first  examined,  and  then  their  properties  will  be  compared. 

432.  Cast  Iron.  —  Cast  iron,  or  pig  iron,  is  the  product 
formed  in  the  blast  furnace   by  the   direct  reduction   of 
iron   ore   with   carbon.     The   ores    employed   are    chiefly 
oxides,  or  carbonates  which  can  readily  be  converted  into 
oxides. 

Carbon,  in  the  form  of  coke  or  charcoal,  is  used  to  re- 
duce the  ferric  oxide,  that  is,  to  separate  the  oxygen  from 
the  iron.  A  material,  called  a  flux,  which  aids  in  the 
reduction  of  the  ore  by  uniting  with  the  earthy  materials 
in  the  ore,  is  also  added.  For  the  sake  of  simplicity,  let 
us  consider  the  impurity  in  the  ore  to  be  silicon  dioxide. 

468 


CAST  IRON 


469 


This  is  an  acidic  oxide  or, 
in  other  words,  the  anhydride 
of  an  acid,  silicic  acid 


SiO, 


H20 


'2       + 
silicon  water 

dioxide 


H2SiO, 

silicic 
acid 


When  silicon  dioxide  is 
heated  to  a  high  temperature 
with  limestone,  the  heat  de- 
composes thd  limestone: 


CaCO3 

calcium 
carbonate 


CO, 


CaO 


'2     + 
.carbon         calcium 
dioxide          oxide 


The  calcium  oxide,  which  is 
a  basic  oxide,  combines  with 
the  acidic  oxide  to  form  a 
salt,  calcium  silicate: 


SiO,    +    CaO 


'2 

silicon 
dioxide 


calcium 
oxide 


CaSiO, 

calcium 
silicate 


The  calcium  silicate,  being 
lighter  than  the  molten  iron, 
separates  and  forms  a  layer 
above  it,  called  slag.  Other 
acidic  oxides,  such  as  the 
oxides  of  phosphorus  and 
sulphur,  would  combine  with 
the  basic  oxide,  and  to  a 
considerable  extent  be  elimi- 
nated in  the  slag. 

Sometimes  the  rock  ma- 
terial in  the  ore  is  limestone 
or  some  other  basic  rock ; 
in  that  case  silica  instead  of 


FIG.  142.  —  BLAST  FURNACE. 
(Sectional.) 


LUMPS  OF  COKE 
LUMPS  OF  IRON  ORE 
LUMPS  OF  LIME 
DROPS  OF  SLAG 
DROPS  OF  IRON 


LAYER  OF  MOLTEN  SLAG 


LAYER  OF  MOLTEN  IRON 


470 


IRON  AND   STEEL 


limestone  is  mixed  with  the  ore  to  produce  the  slag.     The 
slag,  in  addition  to  gathering  the  earthy  material  into  a 

fusible  mass,  forms  a 
temporary  coating  on 
the  drops  of  iron  as  they 
work  their  way  down 
through  the  furnace, 
and  so  protects  them 
from  oxidation. 

A  sectional  drawing 
of  the  form  of  furnace 
commonly  used  in  this 
country  for  making  cast 
iron  is  shown  in  Fig. 
142.  Hot,  dry  air  from 

Copyright  by  the  Keystone  View  Co.  •«.-•• 

the  pipe  "  A     is  forced 

FIG.  143.  —  LADLE  POURING  MOLTEN  CAST       ,  ,  ,  m  », 

IRON  through    nozzles    "  T 

into  the  lower  part  of 

the  furnace.  It  is  this  blast  of  air  which  gives  the  fur- 
nace its  distinguishing 
name  of  blast  furnace. 
The  gaseous  products 
of  combustion  pass 
from  the  furnace 
through  a  pipe  near 
the  top.  The  blast  air, 
combining  with  the 
coke,  raises  the  tem- 
perature of  the  furnace 
to  the  high  degree  at 
which  ferric  oxide  is 
reduced  by  carbon,  and 
the  impurities  in  the 
ore  enter  the  slag.  Fie.  144.  — CHAIN  OF.  MOLDS. 


Copyright  by  the  Keystone  View  Co. 


PIG  IRON 


471 


When  enough  iron  has  accumulated  in  the  lower  part  of 
the  furnace,  the  slag  floating  on  the  iron  is  run  off  through 
the  slag  hole  "  C,"  just  above  the  level  of  the  molten  iron. 
The  iron  is  then  allowed  to  run  out  through  the  tap  hole 
"  H  "  into  a  ladle  which  carries  the  fluid  iron  to  the  casting 
machine.  This  consists  of  molds  of  iron  mounted  on  an 
endless  chain.  A  stream  of  iron  is  poured  into  these  molds 
and  there  solidifies  into  bars,  flat  on  top  and  oval  beneath, 
called  pigs  (Fig.  145). 
From  this  name  the  iron 
is  usually  called  pig 
iron  when  it  is  made. 
The  pouring  is  shown 
in  Fig.  143  and  the 
chain  of  molds  is  shown 
in  Fig.  144.  When  pig 
'iron  has  been  remelted 
in  the  iron  foundry 
(§  440)  and  formed  into 
useful  articles  "by  cast- 
ing in  molds,  it  is  called 
cast  iron. 

Cast  iron  is  the  most 

impure  form  of  iron,  containing  from  2%  to  7.5%  of  car- 
bon, in  addition  to  other  impurities,  the  most  important 
of  which  are  sulphur,  phosphorus,  and  silicon.  Commer- 
cial grades  of  cast  iron  contain  from  3%  to  4.5%  of  car- 
bon. The  carbon  is  partly  combined  with  the  iron  in 
iron  carbide,  Fe3C,  and  partly  scattered  through  the  metal 
in  flakes  of  graphite. 

433.  Nature  of  Steel.  —  Steel  differs  from  cast  iron  in 
composition  in  two  particulars  :  1st,  it  contains  less  than 
2%  carbon;  2d,  none  of  the  carbon  in  steel  is  in  the 


Copyright  by  the  Keystone  View  Co. 

FIG.  145.  —  PIG  IRON  IN  A  METAL  YARD. 


472  IRON  AND   STEEL 

form  of  graphite,  but  is  combined  with  the  iron  in  iron 
carbide,  Fe3C,  which  is  in  solid  solution  in  the  metal. 
The  percentage  of  carbon  in  steel  and  the  heat  treatment 
which  the  steel  has  received  in  its  production  from  cast 
iron,  together  determine  the  properties  of  the  steel 
produced.  When  the  percentage  of  carbon  is  below  0.3  %, 
the  steel  is  known  as  low-carbon,  soft,  or  mild  steel.  With 
0.3  %  to  0.8  %  of  carbon,  the  steel  is  medium-carbon  or  half- 
hard  steel.  From  0.8%  to  2.0%  carbon  produces  high- 
carbon,  hard,  or  tool  steel.  These  limits  are  approximate, 
particularly  with  reference  to  the  hardness,  as  this  prop- 
erty is  largely  modified  by  the  heat  treatment.  The 
manufacture  and  properties  of  the  various  kinds  of  steel 
will  be  discussed  later  in  the  chapter. 

434.  Nature  of  Wrought  Iron.  —  In  the  percentage  of  car- 
bon, wrought  iron  has  the  same  limits  as  low-carbon  steel, 
from  0.05%  to  0.3%.     The  essential  difference  between 
wrought  iron  and  mild  steel  is  the  fact  that  the  manufac- 
ture of  wrought  iron  leaves  a  small  percentage  (0.2%  to 
2.0%)  of  slag  in  the  finished  iron.     The  method  of  work- 
ing wrought  iron  causes  the  slag  to  take  the  form  of  long 
rods  extending  through  the  mass  of  the  iron,  and  so  gives 
wrought  iron  a  fibrous  structure  not  found  in  steel.     The 
latter  is  completely  melted  during  its  formation,  and  the 
slag  rises  to  the  top  and  is  removed  ;  steel,  on  solidifying, 
has  a  crystalline  structure  throughout. 

435.  Bessemer  Process. —  This  process  consists  essentially 
of  removing  from  pig  iron  nearly  all  of  the  impurities  by 
oxidation,  and    then  adding  enough   carbon   to  give  the 
percentage  desired  in  the  steel.     The  molten  iron  from  the 
blast  furnace  is  run  into  a  ladle,  instead  of  into  molds, 
and  is  poured  into  a  huge  pitcher-shaped  vessel,  called  a 
converter.     A  blast  of  air  is  driven  up  through  the  metal 


BESSEMER   PROCESS 


473 


FIG.   146.  —  BESSEMER  CONVERTER. 


in  the  converter  from  the  bottom,  in  order  to  oxidize  the 
impurities.  The  acidic  and  basic  impurities  unite,  while 
the  carbon  is  converted  into  carbon  dioxide.  The  details 
of  the  converter  are 
shown  in  Fig.  146.  The 
heat  liberated  in  the 
process  keeps  the  metal 
fluid,  and  the  action  con- 
tinues until  the  iron  be- 
gins to  oxidize,  a  point 
which  is  indicated  by  a 
change  in  the  color  of 
the  flame.  At  this  in- 
stant a. special  iron,  rich 
in  carbon,  manganese, 
and  silicon,  is  added  to 
the  charge  in  the  converter  in  the  proportion  necessary 
to  give  the  steel  the  desired  composition.  The  manganese 
prevents  the  formation  of  iron  oxide ;  and  the  silicon,  the 
formation  of  bubbles  of  gas,  or  blowholes.  The  action 
is  continued  just  long  enough  to  incorporate  thoroughly 
the  alloy  with  the  metal.  Then  the  converter  is  tipped 
on  its  axle  and  the  steel  run  into  a  ladle,  from  which  it 
is  poured  into  a  series  of  ingot  molds,  standing  on  a 
train  of  cars  near  the  converter. 

The  composition  of  the  converter  lining  affects  the 
character  of  the  steel  produced  and  determines  the  kind  of 
pig  iron  that  may  be  made  into  steel  by  this  process. 
When  the  lining  is  "acid,"  that  is,  composed  chiefly  of 
silica,  only  pig  iron  containing  a  small  proportion  of  phos- 
phorus can  be  employed,  as  the  phosphorus  is  not  burned 
out  under  these  conditions.  With  a  "  basic  lining,"  the 
essential  constituents  of  which  are  calcium  and  magnesium 
oxides,  the  phosphorus  is  more  completely  eliminated, 


474 


IRON  AND   STEEL 


lower-grade  pig  iron  can  be  used,  and  -a  better  quality  of 
steel  produced. 

Since  the  entire  Bessemer  process  occupies  less  than 
half  an  hour  and  as  much  as  20  tons  may  be  handled  in  a 
single  converter,  it  will  be  readily  seen  that  the  product 
will  be  less  uniform  than  that  produced  by  a  slower 
process.  Bessemer  steel  is  used  generally  for  rails  and 
often  for  the  less  important  kinds  of  structural  work. 
Where  a  greater  degree  of  uniformity  and  reliability  is 
required,  steel  made  by  the  slower  open-hearth  process  is 
generally  preferred. 

436.  Open-hearth  Process. —  In  this  process  the  impurities 
in  pig  iron  are  oxidized  by  the  addition  of  iron  oxide  and 


FIG.   147. — OPEN-HEARTH  FURNACE. 


diluted  by  the  addition  of  scrap  steel.  The  charge,  con- 
sisting of  pieces  of  pig  iron,  iron  ore,  and  steel  scrap,  is 
melted  by  the  flame  of  a  mixed  blast  of  air  and  gas,  pass- 


CRUCIBLE  PROCESS  475 

ing  over  the  hearth  of  a  saucer-shaped  furnace  (Fig.  147). 
This  furnace  may  have  either  an  acid  or  a  basic  lining,  as 
in  the  case  of  the  Bessemer  coverter,  with  the  same  differ- 
ences in  the  character  of  the  pig  iron  employed  and  in  the 
composition  of  the  steel  produced.  When  a  basic  lining 
is  employed,  the  slag  produced  contains  phosphates,  which 
are  valuable  as  fertilizer.  As  this  process  fakes  as  many 
hours  as  the  Bessemer  process  does  minutes,  samples  of  the 
product  can  be  withdrawn  at  intervals  and  their  composi- 
tion determined.  Thus  the  character  of  the  product  may 
be  much  better  controlled  than  in  the  coverter. 

In  the  open-hearth  furnace,  there  is  a  pair  of  brickwork 
chambers,  through  which  the  air  and  gas  pass  before  mix- 
ing at  the  mouth  of  the  furnace,  and  a  similar  set  through 
which  the  products  of  combustion  pass  on  their  way  to  the 
chimney,  heating  the  bricks  very  hot  in  their  passage.  By 
reversing  the  direction  of  the  gases  at  intervals,  the  in- 
coming air  and  gas  are  heated  exceedingly  hot  before  they 
meet  and  burn  in  the  furnace.  In  this  way  a  very  intense 
heat  is  produced  in  the  furnace  chamber  with  an  economi- 
cal use  of  fuel. 

Open-hearth  steel  is  used  for  bridges,  armor  plate  and 
the  better  class  of  structural  work,  and  also  for  conversion 
into  the  high-grade  tool  steel. 

437.  High-grade  Steel. —  For  uses  demanding  the  greatest 
uniformity  and  freedom  from  undesirable  impurities,  further 
refining  than  is  obtained  in  the  processes  just  described  is 
necessary.  Of  a  number  of  processes  which  are  in  use,  the 
most  important  are  the  crucible  process  and  the  electric 
furnace  process.  In  the  crucible  process,  wrought  iron  or 
steel  is  remelted  in  a  graphite  crucible,  usually  having  a 
capacity  of  about  100  pounds  (Fig.  148).  When  wrought 
iron  is  used,  the  proper  percentage  of  carbon  is  secured  by 


476  IRON  AND  STEEL 

the  addition  of  charcoal  to  the  iron  before  melting.  As 
very  pure  wrought  iron  can  be  obtained,  a  high  degree  of 
purity  can  be  secured  in  the  steel.  When  steel  is  used 
as  the  crucible  charge,  it  has  usually  been  made  by  heat- 
ing wrought  iron  bars  for  a  long  time  in  contact  with 
carbon  ;  this  results  in  iron  carbide  forming  and  entering 
into  solid  solution  with  the  iron,  chiefly  near  the  surface. 
The  main  object  in  remelting  in  the  crucible  in  this  case 


Courtesy  of  the  Crucible  Steel  Co.  of  America. 

FIG.  148.  —  CRUCIBLE  MELTING  FURNACES. 

is  to  secure  greater  uniformity  in  the  product.  The  cru- 
cible process  is  now  chiefly  used  to  manufacture  various 
alloy  steels,  in  which  nickel,  tungsten,  or  other  metals  are 
introduced  to  secure  special  properties. 

The  crucible  process  is  expensive  when  considerable 
quantities  of  high-grade  steel  are  to  be  made,  and  is  being 
replaced  by  the  electric  furnace  process.  By  this  process 
Bessemer  steel  can  be  quickly  and  cheaply  converted  into 
steel  as  good  as  the  open-hearth  product,  or  open-hearth 


ELECTRIC  FURNACE  PROCESS 


477 


steel  can  be  converted  into  high-grade  steel  in  less  time 
and  at  less  expense  than  by  the  crucible  process.  The 
furnace  proper  is  similar  to  the  open-hearth  furnace, 
and  is  so  arranged  that  it  can  be  tipped  for  pouring  the 
metal  at  the  end  of  the  opera- 
tion (Fig.  128).  Instead  of  the 
elaborate  arrangement  for  heat- 
ing by  gas,  there  are,  in  the 
simplest  form,  two  graphite 
electrodes  which  can  be  lowered 
into  the  slag  floating  on  the 
metal,  which  is  molten  when 
placed  in  the  furnace  (§  403). 
The  resistance  offered  to  the 
current  develops  an  intense 
heat,  and  sulphur  and  phospho- 
rus are  oxidized  by  iron  oxide 
and  lime  that  is  thrown  in  ;  a 

slag  is  formed  on  top  as  a  result  Courtesy  of  the  Crucim  sted  Co- 
of  the  action  of  these  materials 
with  the  impurities  in  the 
metal.  The  carbon  is  almost  entirely  burned  out  and  the 
proper  amount  is  introduced  by  the  use  of  recarbonizing 
alloys,  as  in  the  Bessemer  and  open-hearth  processes.  By 
a  proper  choice  of  the  material  added,  a  high-grade  carbon 
steel  or  alloy  steel  of  any  desired  composition  can  be  pro- 
duced. Amounts  as  high  as  15  tons  can  be  made  at  one 
operation,  which  is  completed  in  2  hours.  The  excellent 
quality  of  the  steel,  the  great  range  of  different  steels  that 
may  be  produced  in  the  same  furnace,  and  the  large  re- 
duction in  the  amount  of  manual  labor  required,  make  it 
probable  that  the  electric  process  will  almost  entirely  re- 
place the  crucible  process,  especially  for  the  manufacture 
of  large  quantities  of  steel. 


FIG.  149.  —  POURING  STEEL 
INGOTS. 


478  IRON  AND   STEEL 

438.  Manufacture  of  Wrought  Iron. —  The  raw  material  of 
wrought  iron,  like  that  of  steel,  is  pig  iron  and  the  process 
is  essentially  a  purifying  process.  The  difference  between 
this  and  the  steel  process  is  that  in  making  wrought  iron 
the  metal  is  never  completely  melted.  The  furnace  used 
is  a  reverberatory  furnace.  The  fire  is  in  a  compartment 
at  one  end  and  the  flames  pass  over  the  hearth  of  the  fur- 
nace, which  lies  beyond.  The  arched  roof  over  the  hearth 
reflects  the  heat  down  upon  the  charge,  as  the  products  of 
combustion  pass  to  the  chimney  beyond  (Fig.  119).  The 
charge  on  the  hearth  consists  of  pig  iron  and  iron  ore 
(iron  oxide).  Under  the  influence  of  the  heat,  the  oxygen 
from  the  ore  oxidizes  the  impurities  in  the  pig  iron  and  the 
ore  is  itself  reduced.  The  impurities  unite  in  a  slag.  By 
constant  stirring  with  iron  rods  through  openings  in  the 
side  of  the  furnace,  the  entire  charge  is  exposed  to  the 
heat  and  the  impurities  in  the  pig  iron  finally  reduced  to 
a  very  small  amount.  Impurities  always  lower  the  melt- 
ing point  of  a  solid.  Pure  iron  has  a  higher  melting  point 
than  impure  iron.  As  the  iron  increases  in  purity,  it 
separates  from  the  impure  mass. 

Since  the  metal  is  only  heated  hot  enough  to  reach  a 
pasty  condition  and  not  to  melt  completely,  the  slag  does  not 
rise  in  a  distinct  layer  to  the  top,  but  permeates  the  entire 
mass.  Near  the  end  of 'the  process  the  workmen  gather 
the  pasty  mass  into  balls.  This  process  is  called  "  pud- 
dling." The  balls  of  iron  are  removed  from  the  furnace 
and,  while  still  hot,  most  of  the  slag  is  squeezed  out  by 
hydraulic  presses  or  by  great  steam  hammers.  As  has  been 
stated,  the  slag  is  not  completely  eliminated,  and  the  re- 
sulting network  of  slag  in  the  iron  after  it  has  been 
hammered  and  rolled,  gives  wrought  iron  its  characteristic 
fibrous  structure.  Aside  from  the  presence  of  the  slag, 
the  percentage  composition  of  wrought  iron  is  essentially 


CASTING   OF  IRON  AND   STEEL 


479 


that  of  low-carbon  steel.  There  is,  however,  a  consider- 
able difference  in  the  properties  of  the  two,  resulting  from 
the  difference  in  physical  structure. 

439.   Effect  of  Impurities  on  the  Melting  Point.  —  As  in  the 

alloys,  the  melting  point  of  iron  is  lowered  by  the  addition 

of  another  metal,  or  of  a  soluble  impurity,  such  as  carbon 

or  iron  carbide.     So  we  find  that  the 

purest    irons    and    steels,    such     as 

wrought  iron  and  low-carbon  steel, 

have     the    highest   melting    points. 

As    the    percentage    of    carbon    in- 

creases,   the    melting    point    drops, 

therefore  the  high  -carbon  steels  have 

lower  melting  points  than  the  low- 

carbon  steels,  while  cast  iron  is  lower 

still.     Pure  iron  has  a  melting  point 

of  about  1500°  C.,  while  1400°  C.  may 

be  taken   as   a  representative  melt- 

ing point  for  high-carbon  steel  and 

1200°  C.  for  cast  iron.     The  lowest 

melting  point  obtained  (1050°  C.)  is 

for  cast  iron  with  4.3%  carbon,  and 

for  higher  percentages  of  carbon  the 

melting    point    rises    again.       This 

minimum  melting  point  corresponds 

to   the    cast   iron   having   the    most 

uniform  structure.     The  commercial 

grades  of  pig  iron  run  from  3  %  to 

4.5       carbon. 


FlGl  150-  —  CupOLA 

FURNACE. 


440.  Casting  of  Iron  and  Steel.—  Iron 

. 

for  casting  is  melted   in    the    cupola 

furnace    (Fig.    150).     This  is  essentially  similar  to  the 

blast  furnace  in  its  general   structure,  although  usually 


480  IRON  AND   STEEL 

much  smaller.  A  mixture  of  pig  iron,  coke,  and  a  little 
limestone  is  used,  and  melted  by  the  use  of  an  air  blast, 
as  in  the  blast  furnace,  although  the  blast  for  the  cupola 
is  not  usually  heated.  When  the  iron  is  in  a  thoroughly 
fluid  state,  it  is  run  off  into  a  ladle.  From  wooden  or 
metal  patterns,  sand  molds  of  the  objects  to  be  cast  have 
been  prepared,  and  the  molten  iron  is  poured  into  these 
from  the  ladle. 

The  metal  for  small  steel  castings  may  be  melted  in  a 
crucible  furnace,  particularly  when  a  special  steel  is  to  be 
used.  Bessemer  steel  may  also  be  cast  immediately  after 
pouring  from  the  converter.  For  most  purposes,  how- 
ever, the  open-hearth  furnace  is  preferred  for  the  prepara- 
tion of  steel  for  casting,  since  the  quality  of  the  steel  can 
be  more  closely  regulated  than  with  the  converter,  and 
the  process  is  less  expensive  than  the  crucible  process. 
Steel  castings  are  often  worked  under  a  drop  hammer 
after  removal  from  the  mold.  They  are  then  called 
drop  forgings. 

• 

441.  Welding.  — This  is  the  process  of  joining,  by  pres- 
sure or  hammering,  two  pieces  of  metal  which  have  been 
heated  sufficiently  to  soften  them  (about  600°  C.),  but 
not  to  melt  them.  To  make  a  successful  weld  the  sur- 
faces to  be  joined  must  be  free  from  oxide,  and  so  some 
flux  (sand  or  borax),  which  will  form  a  very  fluid  slag 
with  the  oxide,  is  commonly  used.  The  hammering  ex- 
pels this  slag  and  allows  the  chemically  clean  surfaces  to 
come  in  contact  and  cohere.  Wrought  iron  can  be  very 
successfully  welded  and  many  of  its  uses  depend  on  this 
property.  Blacksmith's  iron  is  wrought  iron.  Low-car- 
bon steel,  corresponding  in  composition  to  wrought  iron, 
may  also  be  welded,  but  for  satisfactory  work  it  must  be 
very  pure  and  very  soft.  High-carbon  steel  and  cast  iron 


WELDING 


481 


cannot  be  welded  by  ordinary  means,  as  they  do  not  soften 
appreciably  until  very  near  the  melting  point. 


Copyright  by  Underwood  &  Underwood. 

FIG.   151.  —  HEATING  IRON  FOR  WELDING. 

i 

In  general,  the  best  welds  are  obtained  by  using  pieces 
of  the  same  composition.  By  the  use  of  the  electric 
welder,  dissimilar  irons  and  steels  may  be  united.  In  this 
apparatus  the  pieces  of  metal  are  held  together  and  a  very 


482  IRON  AND   STEEL 

heavy  current  of  .electricity  passed  through  the  points  in 
contact.  The  electrical  resistance  at  the  surface  of  con- 
tact causes  sufficient  heat  to  raise  the  ends  of  the  pieces 
to  a  welding  temperature.  In  cases  of  electrical  welding 
of  metals  which  cannot  be  welded  under  the  hammer,  it 
is  probable  that  the  temperature  developed  is  high  enough 
to  melt  them  together  rather  than  to  simply  weld  them. 
This  electric  welding  is  essentially  similar  to  autogenous 
welding  (§  376). 

442.  Malleability  and  Tenacity  of  Iron  and  Steel.  —  Low- 
carbon  iron  and  steel  can  be  rolled  into  bars,  rails,  and 
plates,  and  hammered  into  a  great  variety  of  forms,  even 
when  cold.     As  we  have  seen,   when   these   metals   are 
heated  carefully  they  begin  to  soften  long  before  they 
melt.     So  they  are  forged  by  heating  them  red  hot  and 
then  hammering  them  into  the  desired  form.     This  process 
increases   the   tenacity  of  the  metal  without  making  it 
brittle.     It  is  especially  true  of  wrought  iron,  that  the 
more  it  is  worked,  the  tougher  it  is.     Bars  and  plates  are 
made  by  passing  ingots  through  a  succession  of  pairs  of 
rolls  until  they  attain  the  desired  shape.     The  drawing 
of  iron  and  steel  wire  has  already  been  described  (Chapter 
XVIII,    §  172).     Hard  steel  and  cast   iron  are   neither 
malleable  nor  ductile. 

443.  Hardness  and  Tempering.  —  Differences  in  hardness 
in  iron  and  steel  depend  upon  both  the  carbon  content 
and  the  heat  treatment.     Pure  iron  is  comparatively  soft 
and  iron  carbide  is  exceedingly  hard.     In  general,  there- 
fore, the  higher  the  percentage  of  iron  carbide,  the  harder 
the  iron.     Cast  iron  is  usually  very  hard ;  tool   steel   is 
used  to  cut  mild  steel  and  wrought  iron. 

The   hardness  is   affected  not   only  by  the  amount  of 
carbon  present,  but  by  the  form  in  which  the  carbon  exists 


HARDNESS  AND   TEMPERING  483 

in  the  iron  or  steel.  The  way  in  which  the  carbon  is  held 
in  the  steel  depends  upon  the  heat  treatment  the  steel  has 
received.  When  steel  is  heated  to  a  high  temperature 
and  then  suddenly  cooled,  the  iron  carbide  is  chiefly  re- 
tained in  solid  solution.  This  process  makes  the  steel 
harder,  particularly  when  the  proportion  of  carbon  is  high. 
Sudden  cooling  does  not  allow  time  for  the  change  from 
solid  solution  to  a  mixture  of  iron  and  iron  carbide  to 
take  place.  The  solid  solution  cannot  change  into  a 
mixture  of  iron  and  iron  carbide  at  ordinary  tempera- 
tures. 

If  the  steel  is  now  heated  to  a  temperature  below  that 
at  which  it  was  hardened,  the  increased  temperature  per- 
mits the  change  just  mentioned  to  take  place,  and  the 
steel  is  softened  or  tempered.  The  higher  the  temperature, 
within  certain  limits,  to  which  the  hardened  steel  is  raised, 
the  softer  it  becomes,  because  there  is  more  freedom  to 
change  to  iron  and  iron  carbide  from  the  harder  solid 
solution.  After  tempering,  the  steel  may  be  cooled  quickly 
or  slowly  with  no  great  difference  in  the  final  hardness, 
for  the  greatest  amount  of  the  softening  process  possible 
has  already  taken  place  at  the  high  temperature,  and  as  it 
cools  no  further  change  will  take  place.  The  degree  of 
tempering  is  estimated  by  the  color  of  the  oxide  that  forms 
on  the  surface,  a  straw  yellow  corresponding  to  the  hardest 
steel  and  the  familiar  blue  color  of  saws  corresponding  to  a 
comparatively  soft  steel.  A  watch  spring  illustrates  the 
fact  that  a  steel  heated  to  a  high  temperature  is  not  very 
brittle,  as  it  can  be  bent  nearly  double  before  it  breaks. 
Files,  on  the  other  hand,  which  are  tempered  at  a  low 
temperature,  are  very  brittle.  The  following  table 
shows  the  color  of  the  surface  oxide  and  the  correspond- 
ing temperature  of  tempering,  together  with  the  use  of 
the  steel.  . 


484  IRON  AND   STEEL 

COLOE         TEMPERA/TUBE  STEEL  USED  FOR 

Pale  yellow  430°-450°  Razors 

Full  yellow  470°  Penknives 

Brown  490°-510°  Shears  and  tools  for  brass  work 

Purple  520°  Table  knives 

Blue  530°-570°  Watch  springs  and  sword  blades 

Blue-black  610°  Saws  and  other  woodworking  tools 

444.  Magnetic  Properties.  —  All  varieties  of  iron  and  steel 
show  magnetic  properties  at  ordinary  temperatures,  which 
disappear  when  the  metal  is  heated  to  about  700°  C.  There 
is  a  marked  difference,  however,  between  the  magnetic 
behavior  of  the  low-carbon  and  the  high-carbon  varieties 
of  iron  and  steel.  The  purest  and  softest  grades  of  wrought 
iron  are  magnetized  more  easily  than  any  other  forms  of 
iron,  but  this  magnetism  is  temporary  and,  when  the  iron 
is  removed  from  the  magnetizing  field,  it  has  but  little 
permanent  magnetism.  Low-carbon  steel,  which  has  been 
slowly  cooled,  behaves  in  the  same  way  as  wrought  iron, 
which  it  closely  resembles  in  composition.  High-carbon 
steel,  particularly  when  hardened,  has  very  different  mag- 
netic properties.  Under  the  same  magnetizing  force,  a 
piece  of  high-carbon  steel  will  be  a  much  weaker  magnet 
than  a  piece  of  wrought  iron.  When  the  magnetizing 
force  is  removed,  however,  the  steel  will  retain  a  much 
larger  amount  of  permanent  magnetism.  Therefore  soft 
(low-carbon)  iron  and  steel  are  used  in  making  electro- 
magnets, as  in  motors,  dynamos,  lifting  magnets,  etc. 
These  magnets  may  be  very  strong  when  an  electric  current 
is  passing  through  a  coil  of  insulated  wire  wound  on  the 
iron  core,  but  lose  most  of  their  magnetism  as  soon  as  the 
current  is  cut  off.  When  a  permanent  magnet  is  desired, 
high-carbon  steel,  or  alloy  steel,  is  made  into  the  desired 
form,  hardened,  and  then  magnetized.  Medium-carbon 
steel  and  iron  show  magnetic  properties  intermediate  be- 
tween those  of  the  low-carbon  and  high-carbon  varieties. 


USES   OF  IRON  AND   STEEL  485 

Numerous  physical  experiments  have  led  to  the  con- 
clusion that  magnetizing  a  piece  of  iron  consists  in  turning 
its  molecules  into  a  definite  arrangement.  It  is  believed 
that  only  molecules  of  that  variety  of  pure  iron  which  is 
stable  below  about  700°  C.  can  be  so  rotated.  The  presence 
of  iron  carbide  and  of  iron  with  dissolved  carbon  seems  to 
interfere  with  the  rotation  of  the  molecules.  '  This  would 
account  for  difficulty  in  strongly  magnetizing  cast  iron 
and  high-carbon  steel,  and  also  for  the  retention  of  mag- 
netic power  by  these  metals.  The  presence  of  other  metals, 
such  as  manganese,  in  alloy  steels  often  interferes  with 
the  ease  of  magnetizing  and  demagnetizing.  Permanent 
magnets  are  "  aged  "  by  keeping  them  in  high-temperature 
steam  for  a  considerable  time.  Magnets  so  treated  can 
be  relied  upon  to  maintain  a  constant  strength  for  a  long 
time. 

445.  Uses  of  Iron  and  Steel.  —  Wrought  iron  is  used  for 
wire,  sheet  iron,  ornamental  iron  work,  cores  for  electro- 
magnets, blacksmith's  iron,  cut  nails,  and  other  uses  de- 
manding a  malleable,  ductile  iron,  which  can  be  welded 
and  whose  magnetism  is  temporary. 

Low-carbon  steel  is  used  for  boilers,  tubes,  rivets,  bridge 
work,  ships,  wire,  nails,  sheet  steel,  dynamo  frames,  and 
electrical  castings. 

Medium-carbon  steel  is  employed  in  making  railroad  rails, 
axles,  shafting,  machine  parts,  and  castings.  When  tem- 
pered and  hardened,  it  is  sometimes  used  for  low-grade 
springs  and  cheap  cutlery. 

High-carbon  steel  is  nearly  always  hardened  and  tempered. 
It  is  used  for  cutting  tools,  springs,  files,  etc.  It  is  the 
strongest,  hardest,  most  elastic  and  most  expensive  form 
of  steel. 

Oast  iron  is  used  in  making  pillars,  the  beds  of  machines 


486  IRON  AND   STEEL 

and  castings  in  general.  It  is  also  the  material  which  is 
refined  into  the  other  forms  of  iron  and  steel.  It  is  hard, 
brittle,  and  cheap,  with  high  compressive  strength  and  low 
tensile  strength. 

446.  Alloy  Steels  and  their  Uses.  —  Alloy  steels  are  steels 
containing  other  metals,  whose  presence  gives  them 
especially  valuable  properties.  Nickel,  manganese,  chro- 
mium, molybdenum,  tungsten,  and  vanadium  are  the  chief 
alloy  metals  used.  The  alloy  steels  are  all  hard,  without 
having  the  brittle  qualities  of  high-carbon  steel.  As  each 
has  its  peculiar  excellence,  their  properties  and  uses  will 
be  considered  separately. 

Nickel  steel  contains  about  3%  to  3.5  %  nickel  and  0.25  % 
carbon.  Although  this  is  a  low  percentage  of  carbon,  the 
presence  of  the  nickel  makes  this  steel  at  the  same  time 
very  hard,  very  strong,  very  elastic,  and  very  ductile.  It 
is  used  particularly  for  armor  plate,  bridge  cables,  and  the 
propeller  shafts  of  steamships. 

Manganese  steel  contains  about  12  %  manganese  and  about 
1.5%  carbon.  Its  most  important  property  is  its  very 
great  hardness,  no  matter  what  heat  treatment  it  has 
received.  When  suddenly  cooled,  it  is  very  ductile  ;  when 
slowly  cooled,  it  is  brittle,  so  that  the  rate  of  cooling  has 
an  effect  on  manganese  steel  precisely  the  opposite  of  that 
on  high-carbon  steel.  It  is  used  for  such  purposes  as  safes, 
stone  crushers,  and  the  cross-overs  of  railroad  tracks.  Its 
use  is  limited  by  the  fact  that  it  is  so  hard  that  tools  will 
not  cut  it  and  it  must  be  worked  into  shape  with  emery 
wheels. 

Tungsten  steel  contains  from  5  %  to  10  %  or  even  more  of 
tungsten,  and  from  0.4%  to  2%  of  carbon.  It  makes  very 
good  permanent  magnets,  as  its  retentive  power  is  very 
great.  The  great  hardness  of  this  steel,  even  at  high 


SUMMARY  487 

temperatures,  makes  it  useful  in  "  self-tempering "  or 
"  high-speed  "  metal-cutting  tools.  A  tungsten  steel  tool 
will  cut  without  losing  its  temper,  even  when  the  friction 
developed  is  great  enough  to  raise  the  cutting  edge  to  a 
red  heat.  This  enables  it  to  cut  away  the  metal  much 
more  rapidly  than  a  carbon  steel  tool  would  do. 

Chrome  steel,  with  2  %  chromium  arid  from  0.8  %  to  2  % 
of  carbon,  is  very  hard  and  extremely  elastic  when  suddenly 
cooled.  It  is  the  steel  used  for  the  projectiles  fired  against 
battle  ships.  It  is  employed  in  rock-crushing  machinery 
and  in  safes.  Chromium  is  also  present  in  the  self-temper- 
ing steels. 

Vanadium  steel  combines  elasticity  with  great  tensile 
strength  and  is  much  used  for  automobile  frames  and  parts. 


SUMMARY 

Iron  Ores  are  chiefly  oxides  and  carbonates.  They  are  re- 
duced by  heating  with  coke  in  a  blast  furnace.  Limestone  or 
sand  is  added  to  the  charge  to  convert  the  earthy  impurities  of 
the  ore  into  slag. 

Cast  Iron  (pig  iron)  is  the  product  of  the  blast  furnace.  Many 
articles  are  made  from  pig  iron  and  steel  by  melting  the  metal  in 
a  cupola  furnace,  and  pouring  the  molten  metal  into  molds 
(casting),  i. 

Steel  contains  less  carbon  than  cast  iron,  and  the  carbon  is 
either  combined  as  iron  carbide  or  dissolved  in  the  steel. 

The  Bessemer  Steel  Process  completely  decarbonizes  the  iron 
and  then  the  proper  proportion  of  carbon  is  added. 

The  Open-hearth  Steel  Process  removes  carbon  from  pig  iron 
by  heating  with  iron  oxide  until  only  the  desired  proportion  of 
carbon  remains  in  the  steel. 

High-grade  Special  Steels  are  produced  by  the  crucible  process. 
Much  steel  is  also  made  by  the  use  of  the  electric  furnace. 


488 


IRON  AND   STEEL 


Wrought  Iron  is  made  by  heating  a  mixture  of  pig  iron  and 
iron  ore  in  a  reverberatory  furnace,  with  constant  stirring  and 
working  of  the  pasty  mass  thus  produced.  Wrought  iron  con- 
tains very  little  carbon,  but  contains  some  slag.  Wrought  iron  is 
fibrous  and  tough. 

To  weld  is  to  unite  by  hammering  or  by  pressure  two  pieces 
of  metal  heated  sufficiently  to  soften,  but  not  sufficiently  to  melt 
them.  Wrought  iron  and  low-carbon  steel  can  be  welded. 

COMPARATIVE   TABLE   OF    PROPERTIES 


CAST  IRON 

WROUGHT  IRON 

STEEL 

Low-carbon 

High-carbon 

Carbon,  per 

2%  to  7.5% 

0.05%  to  0.3% 

0.05%  to  0.8% 

0.8%  to  2.0% 

cent 

Melting  point, 

1200°  C. 

1500°C. 

1500°C. 

1400°C.. 

approxi- 

mate 

Structure 

Crystalline 

Fibrous 

Granular  or 

Granular 

fibrous 

Hardness 

Very  hard 

Soft 

Moderately 

Hard,  if  tem- 

soft 

pered 

Possible 

Can  be  cast, 

Can  be 

Can  be  cast 

Can  be  cast 

treatment 

but  not 

welded,  but 

and 

and  tem- 

when 

welded  nor 

not  cast  nor 

welded, 

pered.    Not 

heated 

tempered 

tempered 

but  not 

easily 

tempered 

welded 

Uses 

Castings, 

Wire,  electro- 

Structural 

Tools,  springs 

bases,  and 

magnets 

steel,  wire, 

columns 

and  malle- 

nails, sheet 

able  iron 

steel 

Specific  Properties.  —  Wrought  iron  and  low-carbon  steel  are 
malleable;  cast  iron  is  not.  •  High-carbon  steel  can  be  tempered 
by  heating,  cooling  suddenly,  and  finally  reheating  to  a  tempera- 
ture depending  on  the  degree  of  hardness  desired.  All  varieties 
of  iron  and  steel  can  be  magnetized;  wrought  iron  and  low-carbon 


EXERCISES  489 

steel     most    easily ;     cast    iron   and    high-carbon    steel    most 
permanently. 

Alloy  Steels  are  noted  for  hardness,  strength,  and  ability  to 
retain  their  temper.  The  most  important  metals  combined  with 
iron  in  alloy  steels  are  nickel,  manganese,  tungsten,  chromium, 

and  vanadium. 

0 

EXERCISES 

1.  Why  is  coke  mixed  with  ore  in  a  blast  furnace  instead 
of  being  in  a  firebox  at  the  bottom  ? 

2.  Show  how  the  production  of  slag  is  necessary  to  the  re- 
duction of  the  ore. 

3.  Why  is  an  air  blast  used  in  making  pig  iron  ? 

4.  State  the  essential  differences  in  composition  between 
steel  and  the  other  forms  of  iron. 

5.  Show   how  the  proportion  of  iron  carbide  affects  the 
properties  of  steel. 

6.  Compare  Bessemer  and  open-hearth  steel  as  to  (a)  cost, 
(6)  uniformity,  (c)  strength. 

7.  State  the  relative  advantages  of  the  crucible  and  the 
open-hearth  processes  for  making  high-grade  steel. 

8.  How  does  the  slag  in  wrought  iron  affect  its  structure  ? 

9.  Explain  the  terms :  cupola  furnace,  ladle,  drop  forging. 

10.  What  are  the  advantages  of  electric  welding  ? 

11.  Describe  the  tempering  of  a  table  knife. 

12.  State  and  explain  the  difference  in  magnetic  properties 
between  low-carbon  and  high-carbon  steel. 

13.  Name  ten  articles  of  iron  or  steel  found  in  your  home, 
and  state  in  regard  to  each  whether  it  is  cast  iron,  wrought 
iron,  high-  or  low-carbon  steel. 

14.  State  the  material  used  for  each  of  the  following :  stoves, 
boilers,   wire   fences,   bridges,    saws,   rails,  horseshoes,  sheet 
iron,  nails. 

15.  Give  the  composition,  special  properties,  and  uses  of  two 
alloy  steels. 


CHAPTER   XLI 

LIMB,    CEMENT,  AND  BUILDING  MATERIALS 

447.  Modern  Building  Construction.  —  The  most  notable 
change  in  building  methods  in  recent  years  is  the  great 
increase  in  the  use  of  steel  and  of  concrete  in  structural 
work.  These  materials  are  at  once  strong,  durable,  and 
non-combustible.  It  is  by  their  use  that  huge  fireproof 
buildings  can  be  erected,  without  the  cost  being  prohibi- 
tive. Concrete  consists  of  small  pieces  of  rock  material, 
held  together  by  cement,  so  the  nature  and  properties  of 
cement  must  be  understood  in  order  to  form  a  proper 
opinion  of  what  is  to  be  expected  of  concrete.  The  other 
masons'  materials,  lime,  mortar,  and  stone,  may  be  discussed 
somewhat  more  briefly,  as  they  are  more  familiar. 

448.  Lime.  —  One  of  the  most  abundant  of  rocks  is 
limestone,  which  is  impure  calcium  carbonate,  CaCO3. 
When  this  is  strongly  heated,  it  decomposes;  carbon  diox- 
ide passes  off  as  a  gas  and  calcium  oxide  remains  as  a  hard, 
white  solid : 

CaCO3         — >-  CaO  +  CO2 

calcium  carbonate  calcium  oxide  carbon  dioxide 

Calcium  oxide  is  commonly  known  as  unslaked  lime.  The 
manufacture  of  lime  is  carried  on  in  special  furnaces, 
called  lime  kilns.  These  are  usually  erected  where  lime- 
stone is  found  abundantly  near  the  surface  of  the  ground. 
The  older  types  of  lime  kilns  are  often  set  into  the  side  of 
a  hill,  for  convenience  in  charging  and  removing  the  lime 
after  burning.  The  limestone  and  coal  or  other  fuel  are 


LIME 


491 


FIG.  152.  —  REENFORCED  CONCRETE. 


492      LIME,    CEMENT,   AND  BUILDING  MATERIALS 


mixed  and  fed  into  the  top.  After  the  fuel  has  been  set 
on  fire,  it  is  kept  burning  in  the  lower  part  of  the  kiln  by 
withdrawing  the  burned  lime  from 
time  to  time  and  adding  a  fresh 
charge  at  the  top.  In  this  way  the 
decomposition  starts  high  in  the  kiln 
and  is  completed  when  the  lime- 
stone has  worked  down  to  where 
the  fire  is. 

Lime  formed  in  this  way  is  con- 
taminated with  ashes  from  the  fuel. 
In  the  more  modern  kilns,  the  fires 
are  in  side  chambers  and  only  the 
hot  gases  find  their  way  up  through 
the  charge  of  limestone  (Fig.  153). 
In  this  way  lime  free  from  ashes  is 
obtained. 

The  best  lime  is  made  in  a  rotary 
kiln,  sometimes  as  much  as  150  feet 
long  and  8  feet  in  diameter  (Fig. 

154).  The  limestone  to  be  burned  is  first  crushed  into 
pieces  less  than  an  inch  in  diameter  and  is  then  introduced 
into  the  upper,  cooler  end  of  the  inclined  rotary  kiln  (-BT). 
This  kiln  is  made  of  boiler  plate,  lined  with  fire  brick,  and 
is  caused  to  rotate  by  a  suitable  mechanism.  Into  the  lower 
end  is  introduced  a  blast  of  air  and  producer  gas,  or  pul- 
verized coal,  which  burns  with  an  intensely  hot  flame,  ex- 
tending to  a  considerable  distance  in  the  kiln.  The 
limestone  meets  the  heated  gases  from  the  flame  as  it 
enters  the  upper  end  and  it  gradually  becomes  hotter  and 
hotter  as  it  moves  down  the  kiln  to  meet  the  flame. 
During  this  gradual  rise  of  temperature,  the  moisture  in 
the  stone  is  first  driven  off,  and  then  the  carbon  dioxide 
begins  to  pass  off.  This  process  is  greatly  assisted  by  the 


FIG.   153.  —  LIME  KILN. 


LIME 


493 


constant  turning  over  of  the  pieces,  as  they  work  their 
way  down  the  cylinder,  so  that  when  they  reach  the  in- 
tensely hot  lower  end,  where  the  flame  enters,  the  carbon 
dioxide  has  been  completely  expelled  and  only  calcium 
oxide  remains.  The  hot  lime  is  dropped  from  the  lower 
end  of  the  kiln  into  a  rotary  cooler  ((7),  down  which  it 
passes  in  the  same  way  as  it  passed  through'the  kiln,  and 
is  delivered  at  the  lower  end,  cool  enough  for  immediate 
packing  or  shipment. 

The  fuel  economy  of  this  process  is  very  great.     The 
lime  as  it  moves  down  the  cooler  gives  up  its  heat  to  the 


FIG.   154.  —  ROTARY  LIME  KILN. 

P,  gas  producer  ;  K,  kiln  ;  L,  limestone  bin  ;  D,  dust  chamber  ;  B,  boiler  ; 
C,  cooler ;  .S,  storage  bin  for  lime. 

air  which  entered  at  the  lower  end.  This  heated  air  sup- 
plies the  blast  in  the  kiln  with  oxygen,  and  makes  the 
flame  much  hotter  than  if  cold  air  were  used.  The  heated 
gases  from  the  top  of  the  kiln  are  carried  through  a  dust 
settling  chamber  (2>)  to  the  boiler  (J5),  and  there  generate 
all  the  steam  necessary  for  the  producer,  the  kiln,  and  the 
engines  used  to  rotate  the  kiln  and  drive  other  machinery. 
There  are  few  manufacturing  operations  in  which  there  is 
so  complete  utilization  of  the  heat  generated. 

Lime  made  in  the  rotary  kiln  is  superior  to  that  made 


494      LIME,    CEMENT,   AND  BUILDING  MATERIALS 

by  other  processes,  for  several  reasons.  As  small  pieces 
of  rock  are  used  and  all  the  conditions  of  burning  can  be 
accurately  adjusted,  the  lime  is  burned  throughout,  with- 
out being  overburned,  and  is  free  from  dust  and  ashes. 
It  packs  more  compactly,  and  for  this  reason  is  less  liable 
to  air-slake  than  the  larger  lumps  of  varying  size  produced 
by  the  other  types  of  kiln.  It  is  more  convenient  for  the 
mason  to  handle,  and,  on  the  addition  of  water,  slakes  more 
rapidly  arid  evenly  than  lime  made  by  other  processes. 

Water  unites  with  quicklime  (calcium  oxide)  to  form 
slaked  lime  (calcium  hydroxide): 

CaO         +    H20  — +-    Ca(OH)2 

calcium  oxide  water  calcium  hydroxide 

A  large  amount  of  heat  is  liberated  in  this  operation,  and, 
before  an  excess  of  water  is  used,  steam  may  be  seen  ris- 
ing from  lime  that  is  being  slaked. 

Quicklime  exposed  to  moist  air  unites  with  the  carbon 
dioxide  present,  forming  air-slaked  lime,  which  is  chiefly 
powdered  calcium  carbonate,  since  the  calcium  hydroxide 
first  formed  is  converted  into  the  carbonate : 

Ca(OH)2       +          CO2       — >-CaCO3+H2O 

calcium  hydroxide  carbon  dioxide  calcium         water 

carbonate 

Air  slaking  makes  lime  unfit  for  use  in  mortar. 

449.  Mortar.  —  When  sand  is  thoroughly  mixed  with 
wet,  freshly  slaked  lime,  ordinary  mortar  is  produced. 
Mortar  is  employed  to  form  a  hard,  stony  mass,  which 
holds  together  the  stones  or  bricks  in  a  building.  The 
hardening  of  the  interior  of  mortar  is  chiefly  due  to  the 
escape  of  water.  The  slaked  lime  forms  a  kind  of  jelly- 
like  mass  with  the  water,  in  which  the  grains  of  sand  are 
entangled.  As  the  water  evaporates,  the  calcium  hy- 
droxide hardens  into  a  compact,  stony  mass,  and  the  sand 


CEMENT  495 

gives  additional  strength.  At  the  outer  surface  of  the  mor- 
tar, which  is  exposed  to  the  air,  the  hydroxide  reacts  with 
the  carbon  dioxide  of  the  air,  forming  calcium  carbonate. 
This  action  takes  place  slowly,  and  forms  a  hard  protec- 
tive outer  layer,  which  prevents  water  from  again  entering 
the  mortar  and  softening  the  calcium  hydroxide.  Good 
mortar  strengthens  with  age,  as  shown  by  the  solidity 
of  buildings  erected  centuries  ago.  Cement  is  now  fre- 
quently used  in  place  of  part  or  all  of  the  lime  in  mortar. 

450.  Plaster.  —  The  mortar  .used  for  plastering  formerly 
had  hair  mixed  with  it,  to  give  it  greater  coherence  and 
make  it  less  liable  to  scale  off  when  it  dried  unevenly. 
The  mixture  containing  cement  as  well  as  lime  which  has 
recently  come  into  use  for  plaster,  renders  the  use  of  hair 
unnecessary.     After   the   plaster   has  been   mixed,  it  is 
spread  wet  on  wooden  or  metal  laths  and  allowed  to  be- 
come nearly  dry.     If  a  smooth  finish  is  desired,  the  some- 
what rough  plaster  receives  an  outer  coating  of  powdered 
lime  and  plaster  of  Paris,  worked  into  a  paste  with  water 
and  a  little  glue  or  "sizing."     This  can  be  finished  with 
a  trowel  to  a  smooth  surface,  which  is  hard  when  dry. 

Plaster  of  Paris  is  made  by  roasting  gypsum,  so  as  to 
drive  off  about  three  fourths  of  the  water  of  crystallization 
and  leave  a  fine  powder  : 

2(CaSO4.  2  H2O)  — •>•  (CaSO4)2.  H2O  4-  3  H2O 

gypsum  plaster  of  Paris  water 

When  plaster  of  Paris  is  wet  with  water  and  then  allowed 
to  dry,  it  again  takes  up  water  of  crystallization,  forming 
a  hard,  continuous  mass. 

451.  Cement.  —  Hydraulic  cement  is  made  by  heating  a 
mixture  of  limestone  and  clay  in  a  kiln.     Chalk  or  marl 
may  take  the  place  of  limestone,  since  both  consist  chiefly 


V 

496      LIME,    CEMENT,  AND  BUILDING  MATERIALS 

of  calcium  carbonate.  Shale  or  slate  may  be  substituted 
for  clay,  as  all  three  are  chiefly  aluminum  silicate.  The 
mixture  of  calcium  and  aluminum  silicates  which  con- 
stitutes cement  differs  from  lime  in  two  important  par- 
ticulars :  water  does  not  slake  it,  but  causes  it  to  harden 
or  "  set."  Therefore  cement  and  sand  mixed  form  a  bind- 
ing material  which  will  harden,  even  when  completely 
submerged  in  water. 

In  a  few  localities,  there  exist  deposits  of  "  cement  rock," 
consisting  of  such  a  mixture  of  lime  and  clay  materials 
that  cement  results  from  the  heating  of  the  natural  rock. 
Such  cements  are  known  as  "natural"  cements,  and  are 
usually  inferior  in  quality.  Portland  cement  is  prepared 
from  an  artificial  mixture  of  the  limestone  and  clay  rock 
materials.  The  composition  of  Portland  cement  can  be 
closely  controlled,  and  thus  mixtures  may  be  made  which 
will  yield  the  highest  grade  of  cement.  Slag  cement  con- 
sists of  blast-furnace  slag  mixed  with  slaked  lime. 

452.  Manufacture  of  Cement.  —  Portland  cement  will  be 
taken  as  the  typical  variety,  and  any  points  of  difference 
in  other  varieties  will  be  noted  as  they  occur.  The  rock 
materials  are  carefully  and  thoroughly  ground  to  a  fine 
powder,  first  by  passing  the  rock  through  a  series  of 
chilled  iron  rolls,  and  later  by  tumbling  in  rotating  steel 
cylinders  containing  steel  balls  or  hard,  smooth  pebbles. 
The  different  rock  materials  are  usually  crushed  separately 
at  first  and  thoroughly  mixed  in  carefully  proportioned 
amounts  at  one  of  the  later  stages  of  the  grinding.  For 
.  Portland  cement,  the  proportion  is  about  1  part  of  silica 
and  alumina  (clay  material)  to  3  parts  calcium  carbonate 
(limestone,  chalk,  or  marl). 

Before  "burning,"  the  powdered  mixture  is  dried  by 
heating  in  rotating  drums.  The  kilns  used  in  burning 


SETTING   OF  CEMENT  497 

are  inclined  steel  cylinders,  60  to  150  ft.  long,  lined  with 
fire  brick  and  kept  constantly  rotating,  like  the  rotary  lime 
kiln  described  in  §  448.  The  finely  ground  cement  mix- 
ture is  fed  in  at  the  upper  end,  and  powdered  coal,  or  gas, 
is  forced  in  under  pressure  at  the  lower  end.  The  fuel 
burns  in  a  long  flame,  extending  a  considerable  part  of  the 
length  of  the  kiln.  The  rotation  of  the  kiln,  together 
with  its  inclined  position,  causes  the  rock  mixture  to  work 
gradually  doAVii  from  the  upper,  comparatively  cool,  end 
to  the  intensely  heated  lower  end.  During  their  passage 
through  the  kiln,  the  materials  combine  to  form  a  mix- 
ture of  calcium  and  aluminum  silicates,  which  is  heated 
before  it  leaves  the  kiln  to  a  point  where  it  just  begins  to 
melt.  Natural  cement  is  not  heated  in  its  manufacture 
to  so  high  a  temperature  as  Portland  cement. 

The  finished  material,  as  it  drops  out  of  the  bottom  of 
the  kiln,  is  called  "cement  clinker."  This  clinker  is  first 
cooled  and  then  ground  fine  by  processes  similar  to  those 
described  in  connection  with  the  raw  material.  The 
finished  cement  is  stored  where  it  will  be  as  little  exposed 
to  moisture  as  possible. 

In  the  manufacture  of  slag  cement  there  is  no  burning. 
The  slag,  as  it  flows  from  the  furnace,  is  granulated  by  di- 
recting a  powerful  stream  of  water  against  it.  It  is  then 
dried  and  ground.  Dry  slaked  lime,  which  is  already  a  fine 
powder,  is  added  to  the  partly  ground  slag  and  the  two 
materials  are  ground  together  to  secure  intimate  mixing. 

453.  Setting  of  Cement.  —  When  cement  is  mixed  with 
water  and  the  mass  allowed  to  stand,  it  solidifies  or  "sets." 
The  reaction  that  takes  place  is  probably  a  conversion  of 
the  calcium  and  aluminum  silicates  of  the  dry  cement  into 
other  silicates  of  the  same  metals  containing  combined 
water.  As  the  constituents  of  the  air  have  no  part  in 


498      LIME,    CEMENT,  AND  BUILDING  MATERIALS 

this  reaction,  it  goes  on  as  well  under  water  as  in  the 
air,  and  as  fast  in  the  inside  of  the  mass  as  on  the  out- 
side. The  increase  in  hardness  and  strength  goes  on 
rather  rapidly  during  the  first  few  days  after  the  cement 
is  mixed  with  water,  and  then  more  slowly,  but  the  cement 
continues  to  gain  strength  for  years.  In  fact,  concrete 
buildings  erected  2000  years  ago  are  still  standing  and  are 
probably  stronger  than  when  they  were  built. 

Calcium  hydroxide  is  probably  also  set  free  during  the 
formation  of  the  hydrated  silicates  and  hardens  in  part  by 
the  absorption  of  carbon  dioxide. 

454.  Concrete.  —  Cement  is  seldom  used  alone,  but  is 
mixed  with  sand,  gravel,  broken  stone,  or  cinders  and  water 
to  form  concrete  (Fig.  155).  Concrete  has  not  as  great 
strength  as  pure  cement,  but  pure  cement  would  be  far  too 
expensive  for  use  in  building  construction.  The  usual 
proportion  in  concrete  is  1  part  of  cement  to  3  or  4  parts 
of  rock  material.  This  proportion  may  vary  either  way 
in  any  particular  case,  as  the  use  of  more  cement  will  give 
greater  strength  and  the  use  of  a  larger  proportion  of  stone 
will  make  the  concrete  cheaper. 

The  strength  of  concrete  is  greater  when  made  with 
gravel  than  when  made  with  crushed  and  sifted  stone.  In 
either  case,  the  strength  is  greater  if  the  rock  material  is 
nearly  uniform  in  size  than  if  it  is  not  previously  graded 
by  sifting.  There  is  a  gradual  increase  in  strength  in 
concrete  with  age,  similar  to  that  in  cement,  which  may, 
however,  reach  a  maximum  in  about  six  months  and  then 
fall  off  slightly.  A  good  concrete  will  sustain  a  pressure 
of  between  5000  and  7000  pounds  per  square  inch  measured 
when  the  strength  is  greatest,  without  being  crushed. 

One  advantage  of  concrete  as  a  building  material  is  the 
convenience  with  which  it  may  be  handled.  In  building 


CONCRETE 


499 


a  wall,  for  instance,  the  wet  concrete  is  poured  into  a 
rough  mold  made  of  boards,,  which  may  be  removed,  as 
soon  as  the  concrete  has  set,  and  used  over  again.  Addi- 
tional strength  is  secured  by  setting  up  in  the  molds 


Copyright  by  Underimod  &  Underwood. 

FIG.  155.  —  MAKING  A  NEW  STREET. 

twisted  steel  rods,  running  one  or  both  ways.  The  con- 
crete is  then  poured  in  arid  sets  with  the  rods  firmly 
embedded  in  it.  This  kind  of  construction  is  known  as 
reenforced  concrete  (Fig.  152)  and  is  widely  employed 
in  the  construction  of  buildings,  piers,  and  bridges.  Con- 
crete is  sufficiently  porous  so  that  it  is  not  entirely  water- 


500      LIME,    CEMENT,   AND  BUILDING   MATERIALS 

proof,  but  as  long  as  the  reaction  is  alkaline,  the  steel 
rods  probably  will  not  rust.  We  shall  not  know  defi- 
nitely how  much  danger  of  rusting  there  is  until  our 
reenforced  concrete  structures  have  stood  many  years. 

Cinder  concrete  employs  the  cinders  from  coal  furnaces 
instead  of  rock  material.  The  low  mechanical  strength  of 
the  cinders  makes  this  form  of  concrete  suitable  only  for 
a  nreproofing  material  in  places  where  it  sustains  no  great 


FIG.   156.  —  CONCRETE  WORK  ON  THE  CATSKILL  AQUEDUCT,  NEW  YORK. 

weight,  for  example,  for  a  filling  between  the  floors  of  a 
fireproof  building.  This  is  the  only  kind  of  concrete 
which  can  withstand  without  crumbling  the  sudden  change 
of  temperature  resulting  from  turning  a  stream  of  water 
on  a  burning  building. 

455.  Building  Stone.  —  There  are  3  chief  classes  of  rock 
material  used  for  building  purposes  :  (1)  granites  ;  (2) 
limestones  and  marbles  ;  (3)  sandstones.  The  members 


GRANITE 


501 


of  each  group  have  similar  chemical  composition,  struc- 
ture, and  origin.  The  comparative  strengths  of  differ- 
ent building  stones  is  of  slight  practical  importance,  as 
they  all  have  a  strength  greater  than  that  of  the  mor- 
tar in  which  they  are  laid,  even  if  that  is  a  cement  mor- 
tar. A  far  more  important  property  is  the  extent  to 
which  a  given  building  stone  can  resist  the  action  of  rain, 
sun,  and  frost,  that  is,  its  resistance  to  weathering.  This 
property  is  determined  by  both  its  chemical  composition 
and  physical  structure. 
G-ranitic  rooks  are 
formed  by  the  action  of 
heat  in  the  crust  of  the 
earth,  and  are  very  hard. 
They  consist  of  frag- 
ments 9f  quartz,  feldspar, 
and  mica  welded  to- 
gether into  a  compact 
mass  (Fig.  157).  Quartz 
is  silicon  dioxide,  SiO2  ; 
feldspar  is  a  silicate  of 
aluminum  and  one  or  FIG.  157.  —  HALLOWELL  GRANITE. 
more  alkaline  metals,  and  (Highly  magnified  section.) 

mica  is  of  similar  composition.  As  granite  is  very  com- 
pact, little  water  enters  it,  and  therefore  it  is  little  disin- 
tegrated by  freezing.  None  of  its  constituent  materials  is 
very  soluble  in  water,  and  so  the  rain  does  not  weather  it 
rapidly.  Neither  does  it  break  as  a  result  of  the  variation 
of  temperature  between  hot  days  and  cold  nights.  No 
load  that  it  is  called  upon  to  sustain  permanently  can 
change  its  shape.  As  a  result  of  all  these  properties, 
granite  may  be  regarded  as  the  most  durable  building 
stone.  It  is  also  frequently  of  great  beauty  when  dressed. 
On  the  other  hand,  the  great  hardness  of  granite  makes  it 
difficult  to  dress  and  it  is  too  expensive  for  common  use. 


502      LIME,    CEMENT,   AND  BUILDING  MATERIALS 

Limestone  consists  chiefly  of  calcium  carbonate.  It  is 
formed  by  the  gradual  deposition  of  this  material  under 
water,  or  from  the  disintegration  of  shells.  It  is  a  close- 
grained,  compact  rock,  of  medium  hardness.  Some  lime- 


Copyright  by  Underwood  &  Underwood. 

FIG.   158.  —  MARBLE  QUARRY.     (Concord,  N.H.) 

stones,  called  dolomites,  contain  magnesium  carbonate  as 
well  as  calcium  carbonate.  Marble  is  nearly  pure,  crystal- 
line calcium  carbonate  (Fig.  159),  resulting  from  the  trans- 
formation of  limestone  by  the  pressure  of  rocks  lying 
above  combined  with  the  heat  of  the  earth.  It  is  valued 


SANDSTONE 


503 


FIG.  1 59.  —  MARBLE. 
(Highly  magnified  section.) 


as  a  building  stone  for  the  high  polish  it  takes  and  for  its 

great  beauty.     Limestone  resists  weathering  better  than 

marble,    but    neither    of 

them    is    as    durable    as 

granite.  As  calcium  car- 
bonate is  someAvhat  sol- 
uble in  water  containing 

carbon  dioxide,  the 

weathering  of  limestone 

and  marble  is  chiefly  due 

to  the  dissolving  of  the 

face  of  the  stone.  Neither 

of  these  rocks  is  deformed 

by  any  load  it  is  called 

upon  to  bear. 

Sandstone,  as  its  name 

implies,  consists  of  grains  of  sand  cemented  together  more 

or  less  strongly  (Fig.  160).     The  cementing  materials  are 

silica,  calcium  carbonate, 
iron  oxide,  or  clay.  When 
iron  oxide  is  present,  the 
sandstone  is  red.  There 
are  some  very  durable 
sandstones,  but  they  are 
generally  too  hard  to 
work.  The  sandstones 
which  are  actually  em- 
ployed in  building  are 
comparatively  porous 
and  soft,  They  there- 
FIG.  1 60.  —  SANDSTONE.  fore  weather  badly, 

(Highly  magnified  section.)  breaking  up  particularly 

as  the  result  of  water  getting  into  the  pores  and  freezing. 

The  cementing  materials   between  the  grains  are  often 


504      LIME,    CEMENT,   AND  BUILDING   MATERIALS 

somewhat  soluble  also.  The  elasticity  of  sandstone  is 
very  slight  and  it  takes  a  permanent  set  as  a  result  of 
even  light  loads. 

SUMMARY 

Unslaked  Lime  (quicklime)  is  made  by  roasting  limestone.  It 
is  slaked  by  mixing  it  with  water. 

Mortar  is  a  mixture  of  slaked  lime,  water,  and  sand.  The 
hardening  of  mortar  is  due  to  the  escape  of  water  and  to  the 
reaction  of  calcium  hydroxide  with  the  carbon  dioxide  of  the  air. 

Cement  is  made  by  roasting  a  mixture  of  limestone  and  clay 
materials.  Cement  rock  is  a  natural  mixture  of  these.  Portland 
cement  is  made  from  an  artificial  mixture.  Slag  cement  is  blast 
furnace  slag  mixed  with  slaked  lime.  Cement  materials  are 
ground  fine,  dried,  and  burned  in  rotating  steel  kilns.  The  result- 
ing clinker  is  cooled,  ground  fine,  and  stored  where  it  will  not  be 
exposed  to  moisture.  Cement  consists  of  a  mixture  of  calcium 
and  aluminum  silicates.  It  hardens  by  the  absorption  of  water. 

Concrete  is  cement  mixed  with  sand,  gravel,  broken  stone,  or 
cinders.  It  can  be  conveniently  fashioned  to  any  form  in  molds, 
and  made  very  strong  by  embedding  steel  rods  in  the  mass. 

Cinder  Concrete  consists  of  cement  and  coal  cinders.  Its 
mechanical  strength  is  very  low,  but  it  is  valuable  as  fireproofing. 

The  Most  Important  Building  Stones  are  granites,  limestones 
and  marbles,  and  sandstones. 

Granite  is  very  hard  and  consists  of  quartz,  mica,  and  feldspar. 
It  is  the  most  durable  building  stone. 

Limestone  is  uncrystallized,  and  marble  is  crystallized,  calcium 
carbonate.  Both  are  quite  durable,  but  weather  slowly  by  the 
solvent  action  of  water  containing  carbon  dioxide  on  the  face  of 
the  stone. 

Sandstone  consists  of  grains  of  silica  cemented  together. 
Building  sandstones  are  soft  and  porous.  They  are  not  durable, 
their  weathering  being  due  to  freezing  of  water  in  the  pores. 


EXERCISES  505 


EXERCISES 

1.  Why  is  limestone  more  important  than  any  other  rock 
material  to  the  building  trades  ? 

2.  Distinguish    between    natural    and    Portland    cement. 
Which  is  likely  to  be  the  better  cement  ?     Why  ? 

3.  Describe,  with  the  aid  of  equations,  the  ntanufacture  of 
unslaked  and  slaked  lime. 

4.  What  is  air-slaked  lime  ?     Why  is  it  not  good  for  making 
mortar  ? 

5.  Why  is  whitewash  (lime  and  water)  a  fairly  durable 
inside  wall  covering,  but  not  satisfactory  for  outside  walls  ? 

6.  What  is  mortar?     Explain  what  takes  place  when  it 
sets. 

7.  Why   does   a   mason  cover  the  mortar  in  his  mixing 
trough  with  sand,  if  it  is  not  to  be  used  until  the  next  day  ? 

8.  State  the  difference  between  mortar  and  plaster.     What 
is  "hard  finish"? 

9.  Why  is  cement  mortar  preferable  to  plain  mortar  ? 

10.  Why  are  both  the  cement  materials  and  the  finished 
cement  ground  fine  ? 

11.  Why  do  barrels  containing  lime  often  burst? 

12.  What  happens  in  the  setting  of  cement  ? 

13.  Compare    stone    concrete    with   cinder    concrete    as    to 
materials  and  properties.     What  is  reenforced  concrete  ?     Give 
instances  of  its  use  that  you  have  seen. 

14.  Describe  the  manufacture   of  a  square  concrete  fence 
post  as  you  would  actually  carry  it  out. 

15.  Give  reasons  for  the  increasingly  wide  use  of  concrete. 

16.  Compare  limestone  and  marble  as  building  materials. 
What  are  the  objections  to  sandstone  as  a  building  material  ? 


CHAPTER   XLII 

BRICK  AND  POTTERY 

456.  Clay.  —  Clay  serves  as  the  raw  material  for  a  great 
variety  of  industries,  and  was  one  of  the  first  natural  ma- 
terials to  be  employed  by  man.     It  is  a  silicate  of  alumi- 
num,  formed  by  the  decomposition  of  rocks  containing 
feldspar,  which  consists  of  silicates  of  aluminum  and  an 
alkali  metal.     The  properties  of  clay  which  make  it  so 
valuable  are :  first,  when  mixed  with  water,  clay  forms  a 
plastic  mass,  which  can  be  molded  readily  into  any  de- 
sired form  ;  second,  wlien  baked  to  expel  the  water,  the 
molded   clay   becomes   hard   and    possesses   considerable 
mechanical  strength,  although  it  is  quite  brittle.     So  im- 
pure clays  are  made  into  brick,  drain  and  roofing  tiles, 
common  earthenware  and  stoneware,  while  the  very  pure 
forms,  particularly  kaolin,  are  used  for  the  manufacture  of 
fine  porcelain  and  china. 

457.  Brick.  —  Ordinary  red  bricks  used  for  building  are 
made  from  clay  containing  some  iron  compounds,  and  also, 
usually,  a  certain  amount  of  sand  or  loam.     The  clay  is 
first  pulverized  and  screened  to  rid  it  of  coarse  particles. 
The  desired  amount  of  water  is  then  kneaded  into  the 
clay  in  a  pug  mill.     This  is  a  trough  or  cylinder  with  a 
rotating  shaft  in  the  center,  in  which  are  set  flat  paddles 
arranged  in  a  spiral;  as  the  shaft  turns,   it  thoroughly 
mixes  the  clay  and  water  and  at  the  same  time  forces  it 
along  toward  the  end  of  the  mill.     There  is  a  rectangular 
opening  in  the  end,  which  corresponds  in  shape  and  size 

506 


BRICK 


507 


Copyright  by  Underwood  &  Underwood. 

FIG.    161.  —  GERMAN  QUARRY  WHERE  CLAY  is  OBTAINED   FOR  STEINS  AND 
OTHER  POTTERY. 


508  BRICK  AND  POTTERY 

to  either  the  side  or  the  end  of  a  brick.  The  clay  issues 
from  this  opening  in  the  shape  of  a  rectangular  slab,  and 
is  then  cut  by  wires  into  pieces  of  the  proper  size.  These 
pieces  are  larger  than  the  finished  bricks,  as  considerable 
shrinkage  takes  place  in  drying  and  burning.  The  older 
process  of  molding  the  bricks  individually  by  hand  is 
still  sometimes  followed.  After  either  process,  more 
regular  form  and  greater  density  may  be  given  the  brick 
by  pressing.  Pressed  bricks  are  sometimes  made  directly 
from  the  pugged  clay  without  preliminary  molding. 

After  being  molded,  the  moist  bricks  are  set  on  shelves, 
or  piled  on  each  other,  corncob  fashion,  in  sheds,  where 
they  are  dried  either  by  the  heat  of  the  sun  or  by  air  arti- 
ficially heated,  until  a  large  part  of  the  water  has  evapo- 
rated. They  are  then  piled  in  kilns  in  such  a  way  as  tof 
expose  as  much  as  possible  of  each  one  to  the  heated  gases 
coming  from  a  series  of  fires  built  in  the  outer  part  of  the 
kiln.  This  heating  goes  on  for  days,  until  the  greater 
part  of  the  bricks  in  the  kiln  have  been  properly  burned. 
The  red  color  of  ordinary  bricks  develops  during  burning, 
and  is  the  result  of  the  conversion  of  the  ferrous  com- 
pounds, which  give  the  natural  clay  a  bluish  color,  into  red 
or  brown  ferric  compounds.  Yellow  bricks  are  made  from 
clay  containing  some  magnesium  compounds  but  little  or 
no  iron  compounds. 

The  different  kinds  of  bricks  owe  their  colors  and  other 
properties  to  differences  in  the  materials  from  which  they 
are  made,  and  to  differences  in  manufacture,  particularly 
in  burning.  Vitrified  paving  bricks  are  made  from  clays 
free  from  sand.  The  clay  is  pulverized  much  more  finely 
and  the  temperature  of  the  kiln  becomes  as  high  as  800° 
to  1000°  C.  Vitrified  brick  is  very  close  and  dense  in 
structure  and  the  individual  particles  cannot  be  dis- 
tinguished, for  it  is  heated  in  the  kiln  until  it  just  begins 


POTTERY  509 

to  melt.  Vitrified  brick  is  harder  than  quartz,  and 
makes  a  very  good  paving  material.  The  burning  and 
slow  cooling  of  a  kiln  full  of  these  bricks  takes  about  a 
month. 

Fire  bricks,  used  for  the  lining  of  stoves,  furnaces,  and 
fireplaces,  are  made  from  clay  free  from  iron  and  contain- 
ing a  considerable  amount  of  silica.  They  are  burned  at  a 
temperature  slightly  higher  than  vitrified  bricks.  When 
made  of  suitable  material  and  properly  burned,  they  will 
withstand  the  high  temperature  of  stoves  and  furnaces 
without  either  crumbling  or  softening. 

Terra  cotta  and  hollow  tiles  are  made  of  clays  similar  to 
those  used  in  building  bricks  and  are  burned  in  much  the 
same  way.  Flower  pots  and  other  articles  of  unglazed 
pottery  are  molded  by  hand  or  machine,  and  then  fired. 
Glazed  bricks  have  a  layer  of  pure  white  clay  over  one 
surface,  which  is  then  glazed  by  the  process  described 
below  for  pottery. 

458.  Pottery.  —  Common  pottery  is  made  from  a  grade 
of  clay  considerably  purer  than  that  used  for  bricks,  but 
still  inferior  to  the  kaolins  and  other  fine  clays  used  for 
porcelain  and  china.  For  white  ware  the  clay  must  be 
free  from  iron,  but  it  frequently  contains  undecomposed 
feldspar  and  other  impurities. 

The  clay  is  allowed  to  weather  for  some  time  after  being 
dug,  and  is  then  thoroughly  stirred  with  water  to  allow 
coarse  impurities  to  settle.  The  thin  mud  is  next  strained 
through  fine  sieves,  and  the  clay  is  then  put  into  cloth 
bags  from  which  the  excess  of  water  is  squeezed  out  in  a 
press.  It  is  now  ready  to  be  fashioned  by  the  potter. 

The  chief  contrivance  used  in  pottery  making  is  the 
potter's  wheel.  This  consists  of  two  horizontal  disks  on  a 
vertical  axle,  so  placed  that  when  the  potter  sits  with  the 


510 


BRICK  AND    POTTERY 


Copyright  by  the  Keystone  View  Co. 

FIG.  162.  — POTTER  AT  WORK. 


upper  disk  placed  at  a  convenient  working  height  in  front 
of  him,  he  can  keep  it  in  rotation  by  using  his  feet  on 

the  lower  disk.  Some- 
times the  wheel  is 
driven  by  power,  with 
some  speed-changing 
device  controlled  by 
the  potter's  foot.  A 
lump  of  moist  clay  is 
placed  on  the  wheel, 
which  is  then  set  turn- 
ing, and  the  potter 
fashions  the  clay  into 
any  round  shape  with 
his  moistened  fingers 
(Fig.  162),  or  with 
simple  metal  or  wooden 
tools.  After  this  pre- 
liminary fashioning,  the  wheel  is  stopped  and  any  modifi- 
cation in  shape  is  made,  such  as  adding  a  handle  or 
forming  a  spout.  The  finished  article  is  removed  from 
the  potter's  wheel  and  dried  in  air  for  a  considerable 
time,  and  is  then  fired. 

459.  Varieties  of  Pottery.  —  All  the  varieties  of  clay  man- 
ufactures described  so  far  are  similar,  in  that,  while  un- 
glazed,  they  are  porous  in  structure,  even  after  being  fired. 
A  glaze  not  only  gives  a  smooth  hard  surface,  but  also 
fills  the  pores  and  so  renders  the  articles  water  tight. 
Ordinary  tableware  has  an  earthen,  porous,  opaque  body, 
like  earthenware,  but  it  is  made  of  finer  and  whiter  clays 
and  has  a  finer  glaze,  which  is  often  transparent. 
"  China  "  is  the  name  commonly  given  to  the  finest  grades 
of  ware,  which  usually  have  a  non-porous  body. 


GLAZES  511 

Non-porous  ware  includes  hard  porcelain,  soft  porcelain, 
and  stoneware.  Some  English,  French,  and  Japanese 
chinas  are  soft  porcelain,  but  most  varieties  of  fine  china 
are  hard  porcelain.  The  difference  lies  in  the  kinds  of 
material  employed  and  their  relative  proportion.  Porce- 
lain is  always  translucent.  Stoneware  is  made  of  inferior 
materials,  and  is  used  for  tiles,  pipes,  parts  of  chemical 
manufacturing  apparatus,  and,  with  a  white,  opaque  glaze, 
for  "  porcelain  "  bathroom  fixtures. 

460.  Glazes.  —  The  glaze  on  pottery  and  porcelain  is  a 
hard,  smooth  outer  covering,  resembling  glass.  It  must 
melt  at  a  temperature  not  exceeding  that  required  to 
soften  the  material  on  which  it  is  placed.  The  composi- 
tion of  the  glaze  in  any  particular  case,  and  the  method  of 
applying  it,  depend  upon  the  article  to  be  glazed  and  the 
use  to  which  it  is  to  be  put.  The  glaze  on  cheap  pottery 
is  commonly  a  mixture  of  litharge  and  clay,  which  melts 
in  the  heat  of  the  kiln  to  form  a  lead  glass,  filling  the  pores 
and  forming  a  smooth  surface  coating  for  the  ware.  It 
may  be  sprinkled  on  dry,  or,'as  is  more  commonly  the  case, 
applied  as  a  thin  mud.  Some  cheap  articles  are  glazed  by 
vaporizing  salt  in  the  kiln  daring  burning.  For  common 
earthenware,  the  construction  of  the -kilns  and  the  piling 
of  the  articles  inside  them  is  much  the  same  as  that  de- 
scribed for  bricks. 

The  glazes  used  in  fine  wares  include  a  great  variety  of 
constituents,  each  pottery  having  its  own  favorite  for- 
mulas. It  is  essential  that  the  glaze  shall  expand  and 
contract  at  the  same  rate  as  the  body  of  the  dish.  Some 
glazes  consist  chiefly  of  the  same  material  as  the  body, 
with  just  enough  other  ingredients  to  secure  the  essential 
properties  just  mentioned.  Among  these  other  ingre- 
dients are  included  borax,  lead  compounds,  and  sometimes 
tin  compounds.  The  transparent  glazes  are  usually  borax- 


512  BRICK  AND  POTTERY 

lead  glasses.  The  beauty  of  many  vases  and  other  orna- 
mental pieces  is  chiefly  due  to  glazes  colored  with  mineral 
oxides  which  will  not  decompose  during  firing. 

461.  Manufacture  of  Tableware.  —  The  general  processes 
are  the  same  as  those  described  under  Pottery.     Cups  are 
usually  made  in  plaster  of  Paris  molds,  the  handles  being 
made  separately  and  attached  when  cup  and  handle  are 
still  moist.     Plates  are  pressed  against  a  revolving  form 
on  a  wheel  and  shaped  on  the  bottom  with  a  tool  of  the 
proper  shape.     The  fashioned  articles  are  air  dried,  then 
fired,  then  decorated,  glazed,  and  fired  again.     In   some 
wares,  the  decoration  is  on  the  glaze  instead  of  under  it. 
The  decorative  patterns  on  ordinary  tableware  are  applied 
to  the  article  with  a  rubber  stamp,  or  by  means  of  a  sheet 
of  tissue  paper  on  which  the  design  has  been  printed  from 
an  engraved  plate  with  mineral  colors;  the  paper  is  then 
washed  off,  leaving  the  design  on  the  clay.     Decoration 
under  the  glaze  is  common  in  England  and  on  the  conti- 
nent, while  the  common  American  practice  is  to  decorate 
on  the  glaze.     "Hand-painted"  china  is    nearly  always 
decorated  on  the  glaze.     All  decorated  ware  is  fired  for  a 
considerable  time  after  decoration. 

The  glazes  used  for  tableware  are  usually  harder  than 
those  for  crockery.  For  firing,  the  pieces  are  placed  in 
fire-clay  boxes  called  "  seggers,"  and  the  kiln  is  piled  full 
of  the  seggers.  In  firing  glazed  pieces,  each  piece  must 
be  supported  in  such  a  way  as  not  to  remove  the  glaze. 

462.  Porcelain.  —  Only  the  finest  and  purest  clays,  feld- 
spar, and  other  materials  can  be  used  for  porcelain  manu- 
facture.    The  clays  are  allowed  to  "  ferment "  after  being 
dug,  then  are  ground  and  washed.     The  washed  clay  is 
kneaded    or    rolled  to  make  it   more  uniform,  expel  air 
bubbles,   and    increase   the    plasticity.     The    pieces   are 


PORCELAIN 


513 


molded  on  the  wheel,  or  in  plaster  of  Paris  molds,  or 
they  are  pressed.  They  are  then  dried,  glazed,  and  fired. 
There  is  only  one  firing  for  hard  porcelain,  at  a  very  high 
temperature  (1300°  to  1400°  C.),  and  body  and  glaze 


Copyright  by  Underwood  &  Underwood. 

FIG.  163.  —  KILN  WITH  UNBAKED  POTTERY. 


514  BRICK  AND  POTTERY 

soften  somewhat  under  the  heat  and  unite  to  a  uniform 
glass-like  mass.  Because  of  the  softening,  each  article 
must  be  more  completely  supported  in  the  segger,  and  the 
proportion  of  distorted  pieces  is  much  greater  than  with 
ordinary  tableware. 

English  china  differs  from  other  porcelains  in  containing 
a  large  proportion  of  bone  ash.  It  is  fired  at  a  lower 
temperature  than  the  hard  porcelains,  and  so  is  cheaper  to 
manufacture.  The  glaze  is  a  boric  acid  lead  glass,  having 
a  lower  melting  point  than  the  body  of  the  ware.  French 
soft  porcelain  (Sevres)  is  really  a  glass  ;  it  softens  during 
burning  much  more  than  the  hard  porcelain  and  must  be 
more  carefully  supported.  It  is  glazed  with  a  lead  glass, 
which  forms  a  surface  coating  only. 

Decorative  pottery  is  usually  porous  in  body  and  owes 
its  value  to  its  beauty  of  form  and  to  its  surface  adorn- 
ment. This  may  consist  of  painting  under  the  glaze  or 
upon  the  first  glaze.  Some  of  the  richest  and  most  beau- 
tiful colorings  are  obtained  by  mixing  suitable  metallic 
compounds  with  the  glaze  before  it  is  applied. 

SUMMARY 

Clay  is  a  naturally  occurring  silicate  of  aluminum,  which  is 
plastic  when  wet,  and  hard  when  baked  to  expel  the  water. 

Bricks  are  ordinarily  molded  from  clay  containing  some  iron 
compounds,  dried  in  air,  and  then  baked  in  kilns.  Yellow  bricks 
contain  very  little  iron.  Vitrified  bricks  are  made  from  clay  free 
from  sand,  and  are  burned  very  hard.  Fire  bricks  are  made 
from  clay  free  from  iron,  but  containing  considerable  silica.  Red 
terra  cotta  and  tiles  are  made  from  clay  containing  iron. 

Pottery,  earthenware,  and  china  (porcelain)  are  made  from 
clays  purer  than  those  used  for  bricks.  After  being  fashioned, 
the  articles  are  air  dried,  burned,  glazed,  and  again  burned. 


EXERCISES  515 

The  Glaze  is  a  hard,  smooth,  outer  coating,  resembling  glass. 
It  makes  the  surface  smooth  and  impervious  to  water. 

The  Body  of  bricks,  tiles,  terra  cotta,  pottery,  crockery,  and 
ordinary  tableware  is  porous.  Hard  and  soft  porcelain  (china) 
and  stoneware  have  non-porous  bodies. 

Decorative  Coloring  and  designs  may  be  under,  in,  or  upon  the 
glaze.  The  ware  is  fired  after  decoration. 

EXERCISES 

1.  Give  two  important  properties  of  clay. 

2.  Name  four  kinds  of  brick,  and  give  the  composition  and 
use  of  each  kind. 

3.  What  is  the  difference  in  structure  and  use  between  un- 
glazed  tile  and  vitrified  tile  ? 

4.  Why  is  it  better  to  grow  plants  in  flower  pots  than  in 
glass  jars? 

5.  State  in  order  the  operations  which  a  piece  of  freshly 
dug   clay   undergoes   during   its  conversion  into  a  decorated 
dinner  plate. 

6.  Name  five  articles  which  might  be  fashioned  on  the  pot- 
ter's wheel  ;  two  which  are  otherwise  molded. 

7.  Why  must  a  glaze  have  a  melting  point  lower  than  that 
of  the  article  to  which  it  is  to  be  applied  ? 

8.  Why  is  tableware  always  glazed? 

9.  Why  is  it  unsanitary  to  use  cracked  dishes  ? 

10.  Why  should  the  glaze  when  heated  have  the  same  rate 
of  expansion  as  the  body  of  the  dish  ? 

11.  Under  what  circumstances  would  a  transparent  glaze  be 
used? 

12.  Give  at  least  two  reasons  why  it  is  more  expensive  to 
make  an  undecorated  thin  china  cup  than  a  cup  of  the  same 
capacity  made  of  common  crockery. 

13.  Name  two  characteristic  properties  which  are  common 
to  all  varieties  of  porcelain  and  china. 


CHAPTER   XLIII 
GLASS 

THERE  are  few  substances  that  have  contributed  so 
much  as  glass  to  the  comfort  and  convenience  of  civilized 
life,  as  well  as  to  the  development  of  scientific  knowledge. 
From  the  common  tumbler  or  milk  bottle  to  the  accurately 
ground  lens  of  the  microscope  or  telescope,  the  range  of 
useful  articles  made  from  glass  is  very  large  and  is  con- 
stantly increasing. 

463.  Nature  and  Varieties  of  Glass.  —  Glass  may  be  re- 
garded as  a  solid  solution  of  various  silicates.  By  this 
we  mean  that  the  materials  used  in  glass  making  are  con- 
verted in  the  furnace  into  a  mixture  of  liquid  silicates, 
which  on  cooling  gradually  change  from  a  liquid  condition 
through  a  pasty  state  into  a  solid  mass,  much  as  melted 
wax  does  on  standing  in  the  air.  Properly  made  glass 
shows  no  trace  of  crystalline  or  other  regular  structure, 
but  is  a  hard,  generally  transparent  mass,  the  shape  of 
which  depends  upon  the  conditions  under  which  it  has 
solidified. 

While  there  are  a  great  number  of  special  glasses  de- 
signed for  particular  uses,  it  is  much  easier  to  classify  the 
chief  commercial  varieties  of  glass  than  those  of  porcelain 
or  earthenware.  There  is  always  present  at  least  one  al- 
kaline (sodium  or  potassium)  silicate,  together  with  sili- 
cates of  one  or  more  of  the  metals  calcium,  barium, 
magnesium,  lead,  iron,  aluminum,  etc.  Common  window 
or  bottle  glass  consists  chiefly  of  sodium  and  calcium  sili- 
cates ;  Bohemian  glass,  much  used  for  chemical  glassware, 

516 


MATERIALS  FOR   GLASS  MAKING  517 

is  a  potassium  calcium  glass  ;  flint  glass  is  a  potassium 
lead  glass.  In  addition  to  these  chief  varieties,  there  are 
a  great  number  of  varieties  of  special  glass. 

464.  Materials  for  Glass  Making.  —  The  one  essential 
constituent  for  all  varieties  of  glass  is  "  glass  sand,"  which 
furnishes  the  silica  (SiO2).  Only  the  cleanest  and  whit- 
est of  pure  quartz  sand  can  be  used  in  making  the  best 
grades  of  glass,  but  in  cheap  varieties,  where  freedom  from 
color  is  not  essential,  sand  containing  small  amounts  of 
iron  or  other  impurities  is  sometimes  employed.  Sodium 
sulphate  is  used  in  the  manufacture  of  the  cheaper  grades 
of  glass,  but  for  the  best  quality  sodium  carbonate  is  em- 
ployed, as  it  can  be  obtained  in  a  purer  state.  Potassium 
carbonate  furnishes  the  potassium  for  the  potash  glasses. 
Limestone  is  the  material  most  commonly  employed  to 
furnish  calcium  for  glass.  Many  limestones  consist  of 
practically  pure  calcium  carbonate  and  so  can  be  used  in 
making  the  best  glass.  The  limestone  should  be  as  free 
as  possible  from  magnesia,  and  if  white  (colorless)  glass  is 
to  be  made,  it  should  contain  very  little  iron  —  less  than 

1%. 

When  glass  is  to  contain  barium  in  place  of  calcium, 
either  a  natural  carbonate  (witherite)  or  an  artificially 
prepared  carbonate  is  used.  Flint  glass,  used  for  cut  glass 
and  for  optical  purposes,  contains  lead  in  place  of  calcium 
or  barium.  The  lead  compound  chosen  is  either  red 
lead,  composed  of  PbO  and  PbO2,  or  litharge  (PbO).  The 
red  lead  can  be  obtained  free  from  impurities,  but  as  it 
varies  somewhat  in  the  proportion  of  the  oxides  present, 
an  analysis  is  usually  made,  to  determine  the  proportion 
of  it  to  be  introduced  into  the  mixture.  While  a  large 
number  of  other  materials  are  used  in  glass  manufacture, 
either  as  constituents  added  to  secure  particular  properties, 


518  GLASS 

or  as  a  means  of  eliminating  impurities  in  the  basic  mate- 
rials, the  raw  materials  for  the  chief  varieties  of  glass  are 
as  follows : 

Window  glass  —  sand,  sodium  carbonate  or  sodium  sul- 
phate, limestone. 

Bohemian  glass  —  sand,  potassium  carbonate,  limestone. 

Flint  glass  —  sand,,  potassium  carbonate,  red  lead  (or 
sometimes  barium  carbonate  instead). 

465.  Action  in  the  Glass  Furnace.  —  An  examination  of 
the  materials  just  named  shows  that  in  each  case  they  con- 
sist of  silica  and  basic  oxides,  or  compounds  easily  reduced 
to  basic  oxides.  In  order  that  these  materials  may  react 
to  form  silicates  of  the  metals  present,  they  must  be  ground 
fine,  intimately  mixed,  and  then  raised  to  a  temperature  at 
which  they  will  fuse  together.  When  at  this  high  tem- 
perature, silica,  SiO2,  reacts  with  the  alkaline  carbonates 
to  form  silicates,  with  the  liberation  of  carbon  dioxide. 
A  typical  reaction  would  be  : 

SiO2       +       Na2CO3      — -^  Na2SiO3      +         CO2 

silicon  dioxide          sodium  carbonate          sodium  silicate          carbon  dioxide 

Silicates  of  the  other  metals  are  formed  by  similar  reactions. 
The  fact  that  the  materials  may  be  used  in  different  pro- 
portions and  the  resulting  substance  still  be  recognized  as 
glass,  shows  that  the  molten  mass  is  essentially  similar  to 
a  solution  of  two  miscible  liquids,  such  as  alcohol  and 
water. 

The  intimate  mixing  of  the  melted  materials  is  greatly 
aided  by  the  bubbles  of  carbon  dioxide,  as  they  pass  up 
through  the  viscous  mass.  The  temperature  of  the  furnace 
and  other -conditions  are  so  regulated  as  to  secure  as  large 
bubbles  as  possible.  If  the  bubbles  are  too  small,  the 
glass  will  not  become  sufficiently  fluid  to  allow  them  to 
escape,  so  they  will  remain  as  flaws  in  the  finished  glass. 


STRUCTURE   OF   GLASS  FURNACES 


519 


X" — ^v 


FIG.  164. 


466.  Structure  of  Glass  Furnaces.  —  Two  types  of  furnaces 
are  used  in  glass  manufacture,  according  to  the  use  for 
which  the  glass  is  intended  and  the  quantity 
to  be  made  at  a  time.  In  the  earlier  type, 
the  pot  furnace,  the  materials  were  melted 
in  fire-clay 
pots,  hold- 
ing from 
400  to  4000 

pounds  of  glass.  The 
molding,  drying,  and 
first  heating  of  these 
pots  is  a  delicate  opera- 
tion requiring  many 
weeks  for  its  comple- 
tion ;  after  the  pots  have 
reached  the  full  heat  of 
the  furnace,  they  are 
never  allowed  to  cool  until  it  is  necessary  to  replace 
them.  The  clay  employed  must  be  able  to  stand  ex- 
tremely high  tempera- 
tures without  fusing,  and 
must  react  only  slightly 
with  the  glass  in  the  pot. 
For  fine  grades  of  glass 
the  pot  is  covered  and 
its  only  opening  is  to  the 
outside  of  the  furnace 
(Fig.  164).  The  pots 
are  usually  arranged  in 
a  circle,  walled  about 
and  roofed  over  with  fire 
bricks  (Fig.  165).  The  furnace  is  heated  by  the  burn- 
ing of  a  mixture  of  gas  and  air,  which  has  been  previously 


FIG.   165. — REGENERATIVE  POT  FURNACE. 


RfGENERATOR 


REGENERATOR 


FIG. 


166.  —  REGENERATORS   FOR  HEATING 
GLASS  FURNACE. 


520  GLASS 

heated  by  passing  through  a  hot  checkerwork  of  bricks, 
like  that  employed  in  the  open-hearth  furnace  for  steel 
(Fig.  166). 

The  tank  furnace  (Fig.  167),  used  for  the  manufacture 
of  bottle,  plate,  and  sheet  glass,  is  built  up  of  blocks  of 

fire  clay,  supported  on  a 
suitable  steel  frame,  and 
cemented  together  by  the 
glass  which  flows  into 
the  cracks  from  the  first 

melt  made  in  the  furnace.  It  is  roofed  over  in  the  same 
way  as  the  pot  furnace  and  heated  by  gas  flames  entering 
at  the  side  or  end.  This  furnace  is  continuous  in  opera- 
tion, as  the  raw  material  is  charged  at  one  end  and  the 
finished  glass  is  removed  and  worked  at  the  other  end. 

467.  Chemical  Properties  of  Glass.  —  We  are  accustomed 
to  consider  glass  as  a  stable  substance,  unaffected  by  at- 
mospheric agents  or  by  ordinary  chemicals.  This  is  far 
from  being  the  case,  as  a  comparison  of  old  windowpanes 
with  new  ones,  or  new  bottles  with  those  which  have  con- 
tained "  ammonia  "  or  other  alkaline  solutions,  will  show. 
Even  with  the  most  skilfully  prepared  glass  mixtures,  it 
is  probable  that  there  is  an  excess  of  some  one  or  more  of 
the  constituents  in  the  finished  glass.  If  this  excess  ma- 
terial is  an  alkali,  it  will  react  with  the  carbon  dioxide  of 
the  air  to  form  minute  crystals  of  the  corresponding  alka- 
line carbonate.  This  action  is  of  importance,  since  these 
crystals  are  very  hard,  and,  if  the  glass  is  rubbed  with  a 
dry  cloth,  the  surface  of  the  glass  is  apt  to  be  scratched 
by  these  crystals  and  dulled.  As  the  alkaline  carbonates 
are  readily  soluble  in  water,  the  use  of  a  damp  cloth  will 
prevent  the  injury  of  the  surface  by  these  crystals. 

Water,  as  well  as  carbon  dioxide,  attacks  the  surface  of 


CHEMICAL   PROPERTIES, OF   GLASS  521 

glass  by  dissolving  some  of  the  soluble  materials  which 
happen  to  remain  unaltered.  In  the  case  of  strongly  al- 
kaline glass,  the  water  may  penetrate  below  the  surface, 
and  the  surface  layer  may  eventually  scale  off.  The 
presence  of  specks  of  organic  matter  or  finger  marks  in- 
creases the  liability  of  glass  to  be  attacked  by  both  water 
and  carbon  dioxide.  Eyeglasses  and  other  lenses,  for  ex- 
ample, which  are  allowed  to  become  dusty  or  finger- 
marked, frequently  develop  a  permanent  pitting  of  the 
surface  under  these  marks. 

The  only  acid  having  a  marked  affect  on  glass  is  hydro- 
fluoric acid,  HF.  Like  hydrochloric  acid,  this  is  a  solution 
of  a  gas  in  water.  Either  the  gas  or  the  water  solution 
will  react  with  the  silica  of  the  glass,  according  to  the 
equation  : 

4  HF         +       SiO2      —+        SiF4         +         2  H2O 

hydrofluoric  acid  silica  silicon  fluoride  water 

The  silicon  fluoride  is  soluble  and  can  be  removed  by  wash- 
ing. It  is  necessary  to  keep  hydrofluoric  acid  in  paraffin  or 
gutta  percha  bottles  or  in  lead,  as  it  would  react  with  a 
glass  bottle  and  be  likely  to  eat  its  way  through.  The 
action  just  described  is  made  use  of  in  etching  glass. 
When  the  etched  portion  is  to  be  transparent,  the  solution 
of  hydrofluoric  acid  is  used  ;  and  if  the  surface  is  to  be 
dull,  like  ground  glass,  the  gas  is  employed. 

Strong  alkalies,  like  sodium  and  potassium  hydroxides, 
react  with  the  silica  of  the  bottles  containing  them,  dulling 
the  inner  surface  of  the  bottles  and  sometimes  producing 
a  sediment  in  the  solution.  Ammonium  .hydroxide  acts 
in  the  same  way,  but  to  a  less  extent.  Glass  stoppers  for 
alkali  bottles  should  be  covered  with  grease  or  paraffin, 
since  the  action  of  the  alkali  produces  a  cement  that 
causes  the  stopper  to  stick. 


522  ,          GLASS 

468.  Physical  Properties  of  Glass.  —  Glass  is  always  con- 
sidered a  hard  material,  but  the  different  varieties  show  a 
great  variation  in  this  respect.     In  general,  glass  contain- 
ing a  large  proportion  of  silica  and  lime  is  hard,  while  lead 
and  barium  glasses  are  much  softer.     In  this  connection 
it  should  be  noted  that  flint  glass  is  one  of  the  softest 
varieties,  the  name  being  due  to  the  former  use  of  flints  in 
the  manufacture  of   this  glass  and  not  to  the  proverbial 
hardness  of   flint.      The  hardness  of  glass,  like  that  of 
steel,  depends  upon   the  heat  treatment  it  has  received. 
Sudden  cooling  increases  the  hardness  and  brittleness  ; 
while  slow  cooling  gives  the  glass  a  softer  surface,  but 
greater  ability  to    resist   shock   and  sudden  changes   of 
temperature.     Securing  proper  heat  resistance  for  glass  is 
of  great  importance,  as  glass  is  a  poor  conductor  of  heat 
and  therefore  very  liable  to  crack  if  unequally  heated, 
particularly  if  the  process  of  manufacture  has  left  the 
glass  with  internal  strains. 

To  relieve  these  internal  strains  and  increase  both  the 
mechanical  and  heat  resistance,  nearly  all  varieties  of 
glass  are  annealed  before  being  given  their  final  form. 
The  annealing  ovens  are  so  arranged  that  the  temperature 
of  the  glass  is  changed  very  gradually  from  a  point  just 
below  the  temperature  at  which  it  softens  to  the  temper- 
ature of  the  outside  air.  The  usual  arrangement  is  a 
platform,  on  which  the  glass  is  placed  and  slowly  moved 
through  a  long  chamber,  which  is  hot  at  the  entrance  and 
whose  temperature  gradually  decreases  to  the  exit.  The 
passage  through  this  furnace  consumes  hours,  or  even 
days,  for  the  most  carefully  annealed  glass.  In  special 
cases,  other  means  of  securing  slow  cooling  are  employed. 

469.  Aging  of  Glass.  —  Years  of  exposure  to  light  pro- 
duce color  changes  in  glass  ;    uncolored  glass   becomes 


MANUFACTURE   OF  COMMERCIAL  FORMS      523 


purplish  in  tinge  and  the  tints  of  colored  glass  change  to 
a  certain  extent.  Glass,  on  standing,  also  tends  to  lose  its 
uniform  structure  and  to  become  finely  crystalline  through- 
out. Such  glass  is  unsuitable  for  the  manufacture  of 
chemical  apparatus. 

470.  Manufacture  of  Commercial  Forms.  —  The  majority 
of  glass  objects  are  made  by  either  blowing  or  pressing,  or 
by  a  combination  of  these  processes.  Window  glass  may 
be  taken  as  a  typical  illustration  of  the  blowing  process. 
A  mass  of  the  pasty  glass  is  "  gathered  "  by  rotating  the 
end  of  an  iron  blowpipe  in  the  furnace.  The  blowpipe  is 
then  removed  from  the  furnace,  and  by  a  combination  of 
swinging,  rotating,  and  blowing,  with  a  softening  of  the 
glass  by  reheating  when  necessary,  the  glass  is  made  to 
assume  successively  the  forms  shown  in  Fig.  168.  The 
weight  of  the  glass,  the  centrifugal  force,  and  the  pressure 


FIG.  168.  —  BLOWING  OF  WINDOW  GLASS. 


of  the  air  within  aid  in  the  process.  The  end  of  the  final 
cylinder  is  softened  by  heating,  and  a  rapid  rotation  of  the 
cylinder  on  its  own  axis  causes  the  end  to  open  out.  The 
blowpipe  is  then  detached  from  the  glass,  and  a  crack  made 


524 


GLASS 


lengthwise  in  the  cylinder.  The  split  cylinder  is  now  laid 
on  a  heated  slab  and  gently  flattened  out,  and  finally  passed 
into  the  annealing  oven.  It  will  be  readily  seen  that  any 
bubbles  inclosed  in  the  original  gathering  of  glass  will  ap- 
pear in  the  finished  sheet,  arid  that  uneven  heating,  or 
irregular  rotation,  or  variations  in  the  composition  of  the 
gathering,  will  produce  the  streaks  and  other  irregularities 
so  commonly  seen  in  window  panes. 

A  combination  of  blowing,  shaping  with  tools,  and 
trimming  is  used  in  the  production  of  the  smaller  articles 
of  glassware.  The  steps  in  the  evolution  of  a  blown 
tumbler  will  be  evident  from  Fig.  169.  Thick  tumblers 
are  pressed.  Bottles^  electric  light  bulbs,  and  many  other 


FIG.  169. — STEPS  IN  MAKING  A  GLASS  TUMBLER. 

articles  which  could  not  conveniently  be  completely 
molded,  are  blown  in  molds  (Fig.  170).  In  the  case  of 
bottles,  automatic  machinery  and  compressed  air  are  em- 
ployed to  a  considerable  extent.  Pressed  glass  is  formed 
by  compressing  a  mass  of  viscous  glass  between  a  plunger 
of  the  proper  shape  for  the  inside  of  the  vessel  and  a 
mold.  Much  of  the  imitation  cut  glass  is  made  in  this 


MANUFACTURE   OF  COMMERCIAL  FORMS      525 


way ;  as  pressed  glass  never  has  sharp  edges,  these  are 
secured  by  slightly  cutting  on  a  wheel,  or  by  means  of 
hydrofluoric  acid.  True  cut  glass  is  made  by  first  produc- 
ing the  desired  shape 
in  lead  or  barium  glass, 
with  thick  walls,  and 
then  cutting  in  the  de- 
sign with  a  grinding 
wheel  fed  with  water 
and  emery  powder.  It 
will  be  readily  seen 
that  the  amount  of 
skilled  labor  required, 
and  the  unavoidable 
losses  by  breakage,  to- 
gether with  a  higher 
first  cost  for  material, 
combine  to  make  genu- 
ine cut  glass  expensive. 
In  making  tubing,  the 

glass  is  gathered  and  a  small  cavity  blown  in  the  gather- 
ing, Another  blowpipe  is  then  attached  to  the  opposite 
side  of  the  gathering,  and  the  two  men  holding  the  blow- 
pipes move  apart,  one  of  them  blowing,  at  a  speed  which 
depends  on  the  size  of  the  tubing  to  be  made.  .  By  work- 
ing in  a  tower  one  man  may  be  dispensed  with. 

The  molten  glass  for  plate  glass  is  poured  out  on  a  table 
and  spread  out  by  a  heavy  roller,  running  on  side  rails  of 
such  a  height  from  the  table  as  to  give  the  glass  the  desired 
thickness  (Fig.  171).  When  the  glass  is  hard  enough  to 
remove,  it  is  placed  in  an  annealing  oven  and  annealed  for 
from  4  to  5  days.  It  is  ground  first  to  a  rough  gray  sur- 
face with  sand,  then  to  a  smooth  gray  surface  with  a  finer 
abrasive,  and  finally  polished  to  a  smooth,  brilliant,  per- 


Copyright  by  the  Keystone  View  Co. 

FIG,  170. — DIPPING,  MOLDING,  AND  FIN- 
ISHING NECK  OF  BOTTLE  IN  THE  MOLD 
(FOREGROUND). 


526  GLASS 

fectly  level  surface  with  rouge.     Plate  glass  is  made  in 
sheets  as  large  as  26  by  14  feet. 


Courtesy  of  The  Scientific  American. 

FIG.  171.  —  ROLLING  OUT  PLATE  GLASS. 

471.  Optical  Glass.  —  Glass  for  lenses,  prisms,  and  other 
optical  uses  must  possess  chemical  stability  to  a  very  high 
degree,  it  must  be  free  from  internal  strains,  and  each 
piece  must  be  of  uniform  composition  throughout.  The 
necessity  of  avoiding  dust  and  finger  marks,  and  the  im- 
portance of  cleaning  lenses  with  a  damp  cloth  have  already 
been  referred  to  (§  467).  These  precautions  are  particu- 
larly important  because,  in  general,  the  higher  the  refract- 
ing power  of  glass,  the  softer  the  glass.  A  great  variety 
of  materials  have  been  tried  in  the  endeavor  to  secure  par- 
ticular optical  properties.  To  secure  freedom  from  color 
effects,  it  is  necessary  to  use  compound  lenses  of  at  least 
two  kinds  of  glass.  Single  lenses  are  usually  made  of 
crown  glass,  a  colorless  glass  resembling  window  glass  in 
composition.  The  glass  used  for  color  correction  is  a 


COLORED   GLASS  527 

variety  of  flint  glass,  and  concave  lenses  of  this  material 
are  combined  with  convex  crown  glass  lenses. 

For  optical  glass,  great  care  is  taken  in  the  selection  of 
the  materials,  in  the  manufacture  of  the  covered  melting 
pot,  and  in  the  furnace  treatment,  so  as  to  secure  perfectly 
uniform,  colorless  glass,  free  from  bubbles  and  other  im- 
perfections. When  the  inelt  is  complete,  'the  glass  is 
allowed  to  solidify  in  the  pot.  In  so  doing,  it  commonly 
cracks  up  into  irregularly  shaped  lumps.  The  pot  is 
broken  away,  the  lumps  sorted,  and  the  best  ones  set  aside 
for  lenses.  These  selected  pieces  are  then  softened  by 
heat,  and  each  pressed  into  a  mold  of  the  approximate 
shape  of  the  lens  to  be  made.  The  blanks  thus  secured 
are  then  ground  %  rubbing  against  surfaces  of  the  proper 
curvature,  and  carefully  polished  to  the  exact  shape  de- 
sired. As  only  a  single  piece  can  be  used  for  one  lens,  the 
difficulty  in  securing  a  blank  for  a  large  lens  is  enormous. 
At  best,  only  from  W%  to  20  %  of  the  yield  of  optical  glass 
is  available  for  lenses  of  any  size. 

472.  Colored  Glass.  —  Color  in  glass  may  result  from 
dissolved  compounds,  as,  for  example,  the  iron  compounds 
which  are  present  in  green  bottle  glass;  or  from  finely 
divided  particles.  Ruby  glass  is  an  example  of  the  latter 
method  of  coloring,  owing  its  color  to  extremely  fine  par- 
ticles of  gold  or  of  cuprous  oxide.  Great  care  must  be 
taken  in  coloring  of  this  sort  to  secure  particles  of  the 
proper  size.  By  varying  the  rate  of  cooling,  visible  par- 
ticles, such  as  the  shimmering  flakes  seen  in  some  glass 
marbles,  are  produced.  Where  an  intense  color  is  pro- 
duced by  a  dissolved  compound,  as  in  cobalt  blue  glass, 
lighter  shades  are  obtained  by  "  flashing."  This  consists 
of  coating  white  —  colorless  —  glass  with  a  thin  sheet  of 
the  blue,  and  then  heating  until  the  two  sheets  amalga- 


528  GLASS 

mate.  The  same  result  may  be  attained  by  two  gather- 
ings, the  first  of  the  colorless  and  the  second  of  the  colored 
glass.  Stained  glass  is  made  by  the  use  of  very  fusible 
surface  glazes,  which  are  then  fired  in  a  kiln  at  a  tempera- 
ture high  enough  to  fuse  the  glaze,  but  not  high  enough 
to  soften  the  body  of  the  glass. 

Materials  are  often  added  to  a  mixture  of  ordinary  glass 
materials  to  furnish  a  color  complementary  to  that  produced 
by  some  impurity  already  present  in  the  mixture,  and 
thus  produce  a  colorless  glass.  The  purple  which  man- 
ganese would  produce  alone  is  thus  used  to  neutralize  the 
greenish  tinge  which  iron  would  produce.  The  following 
table  gives  the  colors  and  the  metals  whose  oxides  or  salts 
are  commonly  used  to  produce  them.  By  proper  com- 
binations, almost .  any  color  may  be  produced,  but  the 
results  in  making  colored  glass  are  always  somewhat  un- 
certain, because  of  the  modifications  that  the  heat  treat- 
ment employed  may  produce. 

COLOR  METAL  WHOSE  COMPOUNDS  ARE  USED 

Red-  Cuprous  oxide,  with  or  without  tin  oxide  ;  gold. 

Pink.         Selenium,  in  lead  or  barium  glass. 

Yellow.      Carbon  (finely  divided);   uranium   (fluorescent 

glass) ;   silver,  as  surface  stain  only. 
Brown.      Nickel ;     carbon    (finely   divided) ;     manganese 

and  iron. 

Green.       Chromium  ;  iron. 
Blue.         Cobalt. 
Purple.     Manganese. 
White.       Tin  oxide  ;  aluminum  fluoride  (opalescent). 

473.  Chemical  Glassware.  —Several  kinds  of  glassware 
are  used  in  chemical  laboratories  and  industries.  For 
articles  such  as  test  tubes,  bottles,  and  ordinary  glass 
tubing,  which  are  not  designed  to  be  heated  to  a  high 


SILICA    WARE  529 

temperature,  a  good  soda-lime  glass,  similar  to  window 
glass,  is  employed.  Combustion,  or  hard-glass,  tubing,  in 
which  solids  are  to  be  intensely  heated,  is  made  of  Bo- 
hemian glass,  a  potash-lime  glass,  containing  a  large  pro- 
portion of  lime.  Laboratory  flasks  also  are  usually  made 
of  this  glass.  During  recent  years,  this  combustion  tubing 
has  been  largely  replaced  by  Jena  combustion  tubing.  This 
is  made  at  a  factory  in  Jena,  Germany,  at  which  a  very 
thorough  study  has  been  made  of  the  relation  between  the 
composition  of  glass  and  its  properties,  with  the  result 
that  this  factory  turns  out  a  great  many  varieties  of  glass 
adapted  to  special  uses.  The  Jena  combustion  tubing 
contains  a  considerable  amount  .of  boron  and  some  mag- 
nesium. It  will  sustain  a  very  high  temperature  without 
softening,  and  is  less  liable  to  crack  with  sudden  changes 
of  temperature  than  ordinary  hard  glass.  It  has  the  dis- 
advantage of  growing  gradually  milky  in  appearance  with 
repeated  heating,  and  finally  becomes  practically  opaque 
on  this  account. 

474.  Silica  Ware.  —  The  development  of  high  tempera- 
ture gas  and  electric  furnaces  has  made  possible  the  man- 
ufacture of  a  remarkable  substitute  for  glass.  This  is 
vitrified  silica ;  that  is,  pure  silicon  dioxide  made  plastic 
by  intense  heat  and  fashioned  into  laboratory  ware. 
When  quartz  is  thus  softened  by  an  oxy-hydrogen  or 
oxy-acetylene  blowpipe,  the  result  is  a  transparent  silica 
ware,  resembling  glass  in  appearance.  Vitrified  silica 
expands  much  less  than  glass  when  heated  and  conducts 
heat  much  better.  On  this  account,  it  can  stand  sudden 
changes  in  temperature  much  better  than  Jena  glass.  A 
white-hot  silica  dish  can  be  plunged  into  cold  water  with- 
out cracking.  The  difficulties  of  manufacture  limit  the 
size  of  transparent  silica  articles  and  make  the  price  high. 


530 


GLASS 


When  silica  is  fused  in  an  electric  furnace,  gas  bubbles 
appear,  similar  to  those  formed  when  glass  is  melted. 
These  bubbles  do  not  readily  escape,  and  when  articles  are 
made  of  this  silica,  the  bubbles  are  drawn  out  into  tiny 

tubes  in  the  silica  and 
give  it  a  milky  appear- 
ance (Fig.  172).  This 
opaque  silica  has  prop- 
erties similar  to  the 
transparent  silica,  ex- 
cept that  chemical  ac- 

FIG.  1 72.  -  LABORATORY  SIL.CA  WARE.          fcion  in  an  °Pa(lue  silica 

tube  cannot  be  watched 

like  that  in  transparent  silica.  The  transparent  silica  has 
certain  optical  uses  for  lenses  and  vacuum  tubes  which 
will  transmit  ultra-violet  light,  for  which  naturally  the 
milky  silica  cannot  be  used.  The  electric  furnace  product 
is  much  cheaper  than  the  transparent  silica. 

Silica  ware,  being  composed  of  an  acid  anhydride,  is 
very  rapidly  attacked  by  alkalies,  and  should  never  be  used 
to  contain  an  alkaline  solution  or  a  solid  alkali.  At  or 
above  red  heat,  silica  is  a  strongly  acid  material  in  its 
reactions,  and  on  this  account  is  unsuitable  for  the  fusion 
of  metals. 

The  high  and  definite  melting  point  of  vitrified  silica 
makes  it  valuable  for  tubes  in  electric  laboratory  furnaces, 
as  it  can  be  heated  to  very  high  temperatures  without 
danger  of  melting. 

The  lightest  fibers  used  to  support  the  parts  of  delicate 
instruments  are  made  of  quartz.  The  quartz  is  softened 
with  an  oxygen  blast  lamp,  the  end  of  an  arrow  dipped 
in  it  and  quickly  shot  from  a  bow  down  a  long  passage. 
The  most  difficult  part  of  the  operation  is  to  find  the  tiny 
fiber,  and  to  pick  it  up  without  breaking  it. 


SUMMARY  531 

SUMMARY 

Glass  is  a  solid  solution  of  silicates. 

Window  Glass  consists  chiefly  of  sodium  and  calcium  silicates. 

Bohemian  Glass  consists  chiefly  of  potassium  and  calcium  sili- 
cates. 

Flint  Glass  consists  chiefly  of  potassium  and  lead  or  barium 
silicates. 

The  Materials  used  in  glass  manufacture  are  chiefly  glass  sand, 
sodium  carbonate,  potassium  carbonate,  limestone,  barium  car- 
bonate, red  lead,  and  litharge. 

Manufacture.  —  The  materials  chosen  for  a  particular  glass  are 
ground,  intimately  mixed,  and  heated  in  a  fire-clay  pot  until  they 
fuse  and  react.  In  making  bottle,  plate,  or  sheet  glass,  a  tank 
furnace  is  used.  Glass  furnaces  are  heated  by  gas.  Window 
glass  is  blown  in  cylinders  and  then  flattened  out.  Bottles  and 
many  other  articles  are  blown  in  molds.  Plate  glass  is  rolled 
out,  and  then  ground  to  a  plane  surface.  Glass  is  annealed  by 
slow  cooling,  to  prevent  internal  strains. 

Properties.  —  Glass  is  slightly  soluble  in  water,  and  reacts  with 
carbon  dioxide  and  alkalies.  Lead  and  barium  glasses  are  softer 
than  other  varieties. 

Glass  is  Etched  with  hydrofluoric  acid,  as  this  forms  a  gaseous 
compound  with  the  silica  as  well  as  certain  soluble  fluorides. 

Optical  Glass  is  made  of  special  materials,  and  requires  the 
greatest  care  in  manufacture. 

Colored  Glass  contains  dissolved  metallic  compounds.  Stained 
glass  has  a  colored  surface  glaze  only. 

Combustion  Tubing,  or  hard  glass,  is  either  Bohemian  glass  or 
Jena  glass.  The  Jena  tubing  will  stand  higher  temperatures,  but 
becomes  opaque  on  repeated  heating. 

Silica  may  be  fused  by  the  oxy-hydrogen  blowpipe  or  the  elec- 
tric furnace.  Silica  ware  withstands  high  temperatures  and  sud- 
den changes  of  temperature.  Alkalies  should  never  be  placed  in 
silica  ware. 


532  GLASS. 

EXERCISES 

1.  Give  the  essential  composition  of  glass. 

2.  Distinguish  between  window  glass,  Bohemian  glass,  and 
flint  glass. 

3.  State  what  you  understand  by  a  solid  solution. 

4.  Give  the  materials  used  and  describe  the  manufacture  of 
some  one  kind  of  glass. 

5.  Compare  pot  and  tank  furnaces  as  to  (a)  construction, 
(6)  relative  advantages,  (c)  kind  of  glass  for  which  each  is  used. 

6.  Explain,  using  an  equation,  the  production  of  carbon  di- 
oxide in  glass  making  and  state  how  it  is  eliminated  from  the 
.Finished  glass. 

7.  Why  should  cut  glass  be  cleaned  with  a  soft  cloth  and 
water  that  is  warm,  but  not  hot  ? 

8.  State  the  proper  method  of  cleaning  lenses. 

9.  State  the  effect  on  glass  of  each  of  the  following :  air ; 
water;  alkalies;  hydrofluoric  acid ;  other  acids. 

10.  Describe   the  process  of  annealing  glass   and  state  its 
effect  on  the  properties  of  the  glass. 

11.  Explain    the    presence    of    (a)    bubbles,     (b)    streaks, 
(c)  opaque  particles  in  window  glass. 

12.  Why  is  ruby  glass  commonly  "  flashed  "  ? 

13.  Name  two  properties    particularly  desirable  in   optical 
glass  and  state  how  these  are  secured. 

14.  Give   two   reasons   why  plate  glass  is  more  expensive 
than  ordinary  window  glass. 

15.  Name  three  kinds  of  glass  used  for  chemical  ware. 

16.  Show  how  the  differences  in  the  properties  of  the  three 
kinds  of  chemical  glassware  fit  them  for  their  particular  uses. 

17.  What  is  "  vitrified  silica"  and  how  is  it  made  ? 

18.  In  what  respects  is  vitrified    silica  superior   to  glass? 
Why  does  it  not  replace  glass  entirely  ? 

19.  What  precaution  must  be  taken  in  the  use  of  a  silica 
crucible  ? 


CHAPTER   XLIV 


COMMERCIAL  CHEMICALS. 

475.  Purity  of  Chemicals.  —  In  the  last  fifteen  years  this 
country  has  made  a  marked  advance  in  the  manufacture 
of  chemicals.  Formerly  there 
were  practically  but  two  grades, 
commercial  and  O.  P.  (chemi- 
cally pure).  The  commercial 
grade  was  the  crude  quality 
suitable  for  technical  purposes, 
where  small  amounts  of  other 
compounds  as  impurities  did 
not  greatly  interfere  with  the 
particular  use  of  the  chemical. 
Chemically  pure  chemicals  were 
used  by  druggists  and  for  the 
more  exacting  requirements  of 
the  chemical  laboratory.  Un- 
fortunately, "  C.  P."  did  not 
always  insure  absence  of  im- 
purities. To  meet  the  demand 
for  chemicals  of  undoubted 
purity,  several  firms  began  to 
analyze  each  lot  of  their 
products  and  place  the  analysis 
on  the  label.  These  analyzed 
chemicals  of  tested  purity  have 
been  a  great  aid  to  accurate 
analytical  work,  which  is,  after 

533 


FIG.  173.  —  ANALYZED  CHEMI- 
CAL. 


534  COMMERCIAL    CHEMICALS 

all,  the  regulating  factor  in  chemical  industries  and  most 
useful  in  chemical  education  and  research.  Testing  for 
impurities,  better  knowledge  of  the  theory  of  solutions, 
and  improved  chemical  machinery,  such  as  separators, 
evaporating  pans  and  centrifuges,  have  enabled  manu- 
facturers to  place  chemicals  of  high  purity  on  the  market 
at  a  very  reasonable  price. 

To-day  the  listed  grades  of  chemicals  are  crude,  technical, 
C.  P.,  and  analyzed.  The  technical  quality  is  suitable  for 
most  industrial  purposes  and  the  C.  P.  grade  from  a  reli- 
able manufacturer  serves  well  the  ordinary  purposes  of 
the  chemical  laboratory.  It  is  only  a  question  of  time, 
however,  when  the  C.  P.  grade  will  be  replaced  by 
analyzed  chemicals. 

HYDROCHLORIC  ACID 

476.  Manufacture. — The  manufacture  of  hydrochloric 
acid  grew  out  of  the  manufacture  of  "  salt  cake  "  (sodium 
sulphate),  made  by  heating  common  salt  with  concen- 
trated sulphuric  acid.  The  gaseous  product,  hydrogen 
chloride,  once  allowed  to  escape  into  the  air,  is  now  more 
valuable  than  the  salt  cake. 

The  reaction  takes  place  in  two  stages  : 

NaCl      +      H2SO4    — ^    NaHSO4       +       HC1 

sodium  chloride       sulphuric  acid        sodium  bisulphate       hydrogen  chloride 

NaHSO4     +       NaCl     — >-    Na2SO4      4-       HC1 

sodium  bisulphate     sodium  chloride        sodium  sulphate     hydrogen  chloride 

The  first  action  takes  place  at  ordinary  temperatures, 
but  commercially  it  usually  occurs  in  a  warm  part  of  the 
furnace.  Then  the  cast  iron  retorts  containing  the  mix- 
ture are  pushed  into  a  hot  muffle  or  upon  the  bed  of  a 
reverberatory  furnace,  where  the  second  reaction  is  com- 
pleted. Purer  acid  is  obtained  from  the  first  action  than 


HYDROCHLORIC  ACID  535 

from  the  second.     Accordingly  there  is  a  separate  set  of 
condensers  and  absorbers  for  the  two  grades  of  acid. 

The  hydrogen  chloride  gas  is  led  through  long  cooling 
pipes,  then  through  a  series  of  earthenware  Woulff  bottles, 
and  finally  into  the  bottom  of  tall,  narrow  towers  filled 
with  coke,  over  which  water  flows,  in  order  to  complete 
the  absorption  of  the  hydrogen  chloride  begun  in  the 
Woulff  bottles.  The  dilute  hydrochloric  acid  obtained 
from  the  coke  towers  furnishes  the  absorbing  liquid  for 
the  Woulff  bottles  and  circulates  through  them.  In  this 
way  a  concentrated  acid  is  obtained,  the  most  concen- 
trated coming  from  the  bottles  nearest  the  furnace. 

477.  Properties  of  Hydrochloric  Acid.  —  The  ordinary 
C.  P.  concentrated  hydrochloric  acid  has  a  specific  grav- 
ity of  1.20  and  contains  about  40  %  by  weight  of  dissolved 
hydrogen  chloride  gas.  Commercial  hydrochloric  acid  is 
impure,  and  its  yellow  color  may  be  due  to  traces  of  iron, 
free  chlorine,  or  organic  matter.  It  is  commonly  called 
muriatic  acid. 

When  a  bottle  of  concentrated  hydrochloric  acid  is 
opened  to  the  air,  white  fumes  are  often  seen.  This  fum- 
ing is  due  to  gaseous  hydrogen  chloride  dissolving  in  the 
water  vapor  of  the  air.  The  solution  thus  formed  con- 
denses to  a  white  mist  composed  of  tiny  liquid  particles  of 
hydrochloric  acid. 

Hydrochloric  acid  does  not  react  with  noble  metals, 
like  gold  and  platinum,  and  but  slightly  affects  copper. 
With  lead,  silver,  and  mercury,  its  action  is  also  slight,  as 
these  metals  form  insoluble  chlorides.  -  It  is,  however,  a 
very  active  acid,  dissolving  most  other  metals  with  the 
liberation  of  hydrogen  and  the  formation  of  salts  (§  14). 
Like  all  strong  acids,  it  reacts  vigorously  with  bases  and 
with  most  metallic  oxides  and  decomposes  the  salts  of  less 


COMMERCIAL    CHEMICALS 

active  acids.  Although  minute  quantities  of  hydrochloric 
acid  are  found  in  the  gastric  juice  and  are  essential  to 
good  digestion,  the  acid  is  an  active  poison. 

478.  Uses  of  Hydrochloric  Acid.  —  This  acid  has  a  wide 
range  of  industrial  uses.      Among  the  most  important  are 
the  "  pickling  "  of  iron  before  tinning,  the  preparation  of 
chlorides,  the  production  of  chlorine  used  for  bleaching 
powder  manufacture,  and  the  manufacture  of   glue  and 
gelatine. 

NITRIC   ACID 

479.  Manufacture.  —  The    process    most    used    in   this 
country  for  making  nitric  acid  is  based  upon  the  follow- 
ing reaction  : 

NaN03     +     H2S04   -^   NaHSO4     +     HNO3 

sodium  nitrate        sulphuric  acid        sodium  bisulphate        nitric  acid 

The  mixture  of  niter  and  sulphuric  acid  is  heated  in  an 
iron  retort  at  a  carefully  regulated  temperature,  so  as  not 
to  decompose  the  nitric  acid  formed  and  to  prevent  other 
undesirable  reactions  from  occurring.  The  distillation 
is  stopped  before  all  the  sulphuric  acid  is  used,  so  that 
the  "  niter  cake  "  left  in  the  retorts  may  be  easily  re- 
moved. This  niter  cake  is  used  for  other  purposes. 

The  gaseous  nitric  acid  is  cooled  in  a  series  of  con- 
densers. The  liquid  obtained  has  a  yellowish  tinge,  due 
to  dissolved  oxides  of  nitrogen  formed  by  the  decompo- 
sition of  a  little  of  the  nitric  acid  in  the  process  of  dis- 
tillation. It  may  also  contain  chlorine  if  the  niter 
contained  any  salt. 

To  decolorize  (" bleach")  the  condensed  acid,  air  is 
blown  through  it,  thus  liberating  the  gaseous  impurities. 
The  oxygen  of  the  air  converts  the  lower  oxides  of 
nitrogen  into  the  higher  ones,  which  are  absorbed  by  the 


NITRIC   ACID  537 

water  with  the  formation  of  more  nitric  acid.  The  actual 
process  is  an  ingenious  but  complicated  one. 

480.  Packing  and  Storage  of  Nitric  Acid.  —  Concentrated 
nitric  acid  of  commerce  has  a  specific  gravity  of  1.42  and 
contains  about  70  %  by  weight  of  hydrogen  nitrate,  HNO3. 
It  is  stored  in  stone  pots,  but  is  commonly  shipped  either 
in  carboys  containing  about  120  pounds  of  the  acid,  or 
in  7  pound  glass-stoppered  bottles.      On  account  of  the 
powerful  oxidizing  action  of  nitric  acid,  it  should  never 
be  allowed  to  come  in  contact  with  inflammable  material 
such  as  straw  or  wood.     Neither  should  nitric   acid   be 
stored  near  easily  oxidizable  chemicals,  as   an  oxidizing 
agent  and  a  combustible  material  near  together  form  a 
source  of  great  danger  if  a  fire  starts. 

481.  Properties  of  Nitric  Acid.  — Pure  hydrogen  nitrate, 
HNO3,  is  a  colorless  liquid,  boiling  at  86°  C.     Nitric  acid 
is  the  water  solution  of  this   compound  and  its  boiling 
point  depends  upon  the  amount  of  dilution.     A  solution 
containing  68  %  of  hydrogen  nitrate  boils  constantly  at 
120°  C. 

When  concentrated  nitric  acid  is  heated,  the  following 
decomposition  occurs  : 

4HN03— >-2H20     +     4N02     +     O2 

nitric  acid  water  nitrogen  oxygen 

peroxide 

Sunlight  also  causes  this  reaction.  Bottles  of  the  acid 
standing  near  windows  often  become  yellowish  red,  on 
account  of  the  red  nitrogen  peroxide  liberated  in  the 
liquid. 

Nitric  acid  is  one  of  the  most  active  acids.  It  reacts 
readily  with  most  metals,  but  attacks  neither  platinum 
nor  gold.  Imitation  gold  jewelry  is  often  detected  by 
putting  a  drop  of  the  concentrated  acid  upon  it.  Unlike 


538  COMMERCIAL   CHEMICALS 

many  acids,  hydrogen  is  seldom  obtained  by  the  reaction 
of  nitric  acid  with  metals.  The  hydrogen  at  the  moment 
of  its  liberation  is  oxidized  to  water  by  oxygen  from  other 
nitric  acid  molecules.  When  the  acid  is  very  concen- 
trated, the  following  reaction  occurs  with  most  metals : 

H  +  HNO3  — >-   H2O  +          NO2 

nascent  hydrogen  nitric  acid  water  nitrogen  peroxide 

When  the  acid  is  somewhat  diluted,  nitric  oxide  is  fre- 
quently obtained : 

3  H          +   HN03  — >•   2  H20  +      NO 

nascent  hydrogen         nitric  acid  water  nitric  oxide 

Certain  concentrations  may  give  a  mixture  of  the  nitric 
oxide  and  the  nitrogen  peroxide.  These  compounds  are 
called  reduction  products  of  nitric  acid,  as  they  are  formed 
as  a  result  of  nascent  hydrogen  taking  oxygen  away  from 
the  acid  molecule.  With  very  dilute  nitric  acid,  the 
reduction  product  may  be  ammonia,  which  would  unite 
with  the  excess  of  nitric  acid  present  to  form  ammonium 
nitrate.  The  reaction  which  takes  place  between  nitric 
acid  and  a  metal  depends  upon  the  metal  used,  the  con- 
centration of  the  acid,  and  the  temperature. 

It  is  to  be  remembered,  then,  that  nitric  acid  very 
rarely  gives  hydrogen  when  reacting  with  a  metal,  as  the 
oxidizing  action  of  the  acid  converts  the  hydrogen  into 
water.  The  oxidizing  power  of  nitric  acid  is  shown  in 
many  other  reactions.  Hot  charcoal  burns  in  the  hot  con- 
centrated acid,  an  ordinary  gas  flame  burns  readily  in 
the  hot  acid  vapor;  most  organic  compounds  are  vigorously 
attacked  by  nitric  acid.  The  concentrated  acid  makes 
holes  in  clothing  and  makes  yellow  spots  on  the  skin. 

482.  Uses  of  Nitric  Acid.  —  The  acid  is  of  great  industrial 
importance,  particularly  in  the  manufacture  of  nitro- 


SULPHURIC  ACID  539 

glycerine,  gun  cotton,  smokeless  powder,  celluloid,  and 
many  other  organic  compounds.  Its  salts  are  important 
as  fertilizers,  in  electroplating,  and  in  the  manufacture  of 
fireworks. 

An  important  laboratory  use  is  in  aqua  regia,  a  mixture 
of  three  parts  by  volume  of  concentrated  hydrochloric  acid 
to  one  part  of  concentrated  nitric  acid.  This  mixture 
dissolves  gold  and  platinum,  owing  to  the  liberation  of 
nascent  chlorine  due  to  the  oxidizing  action  of  nitric  acid: 

3HC1      +      HN03    — >-    3C1      +      2H20     +     NO 

hydrochloric  nitric  nascent  water  nitric 

acid  acid  chloride  oxide 

483.  Nitric  Acid  from  the  Air.  —  The  formation  of  nitric 
acid  and  nitrates  by  the  fixation  of  atmospheric  nitrogen 
is  discussed  in  Chapter  XLVI,  §  513.     By  this  method, 
nitrogen  and  oxygen  of  the  air  are  combined  by  means  of 
the  electric  arc.     A  number  of  processes  based  upon  this 
principle  have  been  devised,  but  it  appears  at  present  that 
none  of  them  will  be  able  to  compete  in  the  production 
of  concentrated  nitric  acid,  unless*  the   manufacturer  has 
abundant  water  power  at  his  disposal  for  the  cheap  produc- 
tion of  electricity.     The  process  is,  however,  a  commercial 
success  in  producing  dilute  nitric  acid  and  particularly  a 
supply  of  calcium  nitrate,  a  most  valuable  fertilizer.     Until 
the  great  nite'r  beds  of  Chili  are  exhausted,  a  large  part  of 
the   world's   concentrated  nitric  acid  will  be  made  from 
sodium  nitrate. 

SULPHURIC   ACID 

484.  Manufacture  by  Contact  Process.  —  This   process   is 
based  upon  four  reactions:   the  burning  of  sulphur;  the 
oxidation,  by  a  catalytic  agent,  of  the  sulphur  dioxide 
to  sulphur  trioxide;  the  absorption  of  the  sulphur  trioxide 


540  COMMERCIAL    CHEMICALS 

by  concentrated  sulphuric  acid;  and  finally  the  dilution  of 
the  last  product  with  water: 

S  +  02  — ^  S02 

sulphur  oxygen  sulphur  dioxide 

2SO2  +  O2  -+  2SO3 

sulphur  dioxide  oxygen  sulphur  trioxide 

S03  +          H2S04        — ^         H2S04.S03 

sulphur  trioxide  sulphuric  acid 

H2SO4.SO3        +  H2O          -^-  2H2SO4 

water  sulphuric  acid 

Instead  of  making  use  of  the  last  two  steps,  it  might  be 
thought  that  sulphur  trioxide  could  be  absorbed  directly 
by  water: 

H20  +  S03          — ^  H2S04 

water  sulphur  trioxide  sulphuric  acid 

In  practice,  however,  it  has  been  found  that  the  sulphur 
trioxide  formed  by  the  contact  process  is  not  readily  soluble 
in  water. 

485.  Development  of  the  Contact  Process.  —  The  contact  pro- 
cess has  been  known  for  a  hundred  years,  but  only  within 
the  past  20  years  has  it  become  a  commercial  success. 
Certain  difficulties  had  to  be  overcome  before  the  labora- 
tory reactions  could  be  conducted  profitably  on  a  manu- 
facturing scale. 

For  a  long  time  the  necessity  for  an  excess  of  air 
(oxygen)  was  not  recognized.  Secondly,  in  the  labora- 
tory the  union  of  sulphur  dioxide  and  oxygen  took  place 
almost  completely,  while  in  the  factory  it  was  found  that  after 
a  time  the  platinum  lost  its  effectiveness  as  a  contact  agent. 
This  poisoning  of  the  platinum  was  found  to  be  due  to 
the  action  of  arsenic  trioxide  and  other  compounds  present 
as  impurities  in  the  sulphur  dioxide  gas.  It  was  necessary 
to  devise  means  of  removing  these  before  admitting  the 


SULPHURIC  ACID  541 

gas  to  the  contact  chambers.  Finally  came  the  recogni- 
tion of  the  necessity  for  careful  regulation  of  the  tempera- 
ture, as  the  following  reaction  is  reversible: 

2S02  +  02  ^±  2S03 

sulphur  dioxide  oxygen  sulphur  trioxide 

The  catalytic  union  of  the  dioxide  and  oxygen  takes  place 
most  completely  between  400°  C.  and  450°  C.  At  higher 
temperatures  the  reaction  tends  to  proceed  in  the  opposite 
direction.  Moreover  the  union  of  the  dioxide  and  oxygen 
produces,  heat.  This  difficulty  was  solved  by  using  this 
heat  to  bring  the  incoming  gases  to  the  proper  reaction 
temperature. 

486.  Manufacture  by  Chamber  Process.  —  For  more  than 
a  century  all  of  the  sulphuric  acid  used  for  commercial 
purposes  was  made  by  the  chamber  process.  To-day,  ow- 
ing to  patents  on  the  most  approved  forms  of  apparatus 
for  carrying  on  the  contact  process,  and  to  the  fact  that 
manufacturers  dislike  to  abandon  expensive  equipment  in 
good  working  order,  the  chamber  process  is  still  very  ex- 
tensively used  for  the  manufacture  of  commercial  oil  of 
vitriol.  The  commercial  acid  produced  by  this  process  is 
not  pure  and  is  not  concentrated.  It  contains  only  about 
60  %  to  70  %  of  sulphuric  acid.  The  advantage  of  the 
contact  process  over  the  chamber  process  is  that  the  former 
directly  produces  a  concentrated,  pure  acid. 

The  sulphur  dioxide  used  in  the  manufacture  of  sul- 
phuric acid  is  often  obtained  by  heating  in  contact  with 
air  some  sulphide  of  a  metal,  usually  iron  sulphide 
(pyrites).  The  sulphur  dioxide  is  converted  into  the 
higher  oxide  by  making  use  of  nitrogen  peroxide.  The 
peroxide  is  obtained  by  the  action  of  air  with  nitric  oxide  : 
2NO  +  O  —  *- 


nitric         oxygen  nitrogen 

oxide  peroxide 


542 


COMMERCIAL   CHEMICALS 


SULPHURIC  ACID  543 

The  nitric  oxide  results  from  the  reaction  of  nitric  acid 
with  water  and  sulphur  dioxide.  The  nitric  acid  is  made 
by  the  action  of  sulphuric  acid  with  sodium  nitrate  in 
vessels  called  niter  pots. 

Sulphur  dioxide  mixed  with  nitrogen  peroxide  is  passed 
through  a  tower  called  the  Glover  tower,  to  be  described 
later,  and  then  into  large  lead  chambers.  "  Within  the 
chambers  sulphur  dioxide,  nitric  oxide,  nitrogen  peroxide, 
air,  and  steam  are  brought  together.  Complicated  reac- 
tions take  place  which  are  not  well  understood. 

Since  approximately  four-fifths  of  the  air  is  nitrogen,  it 
is  necessary  to  provide  for  the  escape  of  the  nitrogen  and 
at  the  same  time  prevent  the  escape  of  the  oxides  of  nitro- 
gen as  far  as  possible.  This  is  accomplished  by  causing 
the  chamber  gases  to  pass  through  the  Gay-Lussac  tower. 
The  tower  is  filled  with  coke.  Concentrated  sulphuric 
acid  (78  %  H2SO4)  is  conveyed  to  the  top  of  the  tower 
and  sprinkled  on  the  coke.  The  chamber  gases  enter  the 
tower  at  the  bottom  and  ascend  -against  the  stream  of  sul- 
phuric acid.  When  the  plant  is  running  properly,  prac- 
tically all  of  the  oxides  of  nitrogen  are  dissolved  in  the 
sulphuric  acid.  In  this  manner  they  are  caught  in  the 
Gay-Lussac  tower,  while  the  nitrogen,  being  insoluble 
in  the  acid,  escapes. 

From  the  bottom  of  the  Gay-Lussac  tower  the  sulphuric 
acid,  carrying  in  solution  the  oxides  of  nitrogen,  is  pumped 
to  a  tank  on  the  top  of  another  tower,  called  the  Glover 
tower,  situated  between  the  ore  roasters  and  the  chambers. 
The  Glover  tower  is  similar  in  construction  to  the  Gay- 
Lussac  tower.  It  is  filled  with  lumps  of  quartz.  At  the 
top  of  the  tower  are  two  tanks,  one  containing  the  liquid 
coming  from  the  Gay-Lussac  tower,  and  the  other  the 
chamber  acid  (55%  H2SO4).  As  a  mixture  of  these  two 
liquids  passes  down  through  the  Glover  tower,  it  meets 


544  COMMERCIAL   CHEMICALS 

the  hot  gases  coming  from  the  ore  roasters  and  from  the 
nitric  acid  plant,  on  their  way  to  the  lead  chambers.  The 
result  is  that  the  dilute  chamber  acid  is  made  more  con- 
centrated, the  Gay-Lussac  acid  is  decomposed  by  the  water 
in  the  chamber  acid,  and  the  oxides  of  nitrogen  liberated 
are  allowed  to  enter  the  chambers,  while  sulphuric  acid 
(67  %)  is  obtained  from  the  bottom  of  the  tower.  This 
chamber  acid  can  be  concentrated  by  boiling  in  iron  pans 
and  then  in  platinum  pans,  but  for  many  commercial  pur- 
poses needs  no  further  treatment. 

487.  Storage  and  Packing.  —  Concentrated  sulphuric  acid 
is  usually  stored  in  riveted  steel  tanks ;    the  less  concen- 
trated grades  are  run  into  lead-lined  wooden  tanks.     The 
acid  is  shipped  in  steel  tank  cars  holding  from  30  to  80 
tons,  or  in  steel  drums  containing  from  500  to  1500  pounds. 
The  smaller  quantities  for  laboratory  use  are  sent  in  carboys 
(large  glass  bottles  packed  in  wooden  cases)  containing 
about  200  pounds. 

488.  Physical  Properties.  —  Concentrated  sulphuric  acid 
is  a  heavy,  oily  liquid,  nearly  twice  as  dense  as  water. 
Oil  of  vitriol  is  the  commercial  name  of  the  acid,  derived 
from  an   early  method   of   manufacture  —  distillation   of 
green  vitriol,  FeSO4.7H2O.     The  acid  is  miscible  with 
water  in  all  proportions,  but  great  care  must  be  taken  in 
the   mixing    (§  19).     The   high  boiling   point,    338°  C., 
of  sulphuric  acid  makes  it  valuable  for  use  in  the  prepara- 
tion of  many  other  acids. 

489.  Chemical  Properties.  —  In  general,  sulphuric  acid  is 
not  so  active  an  acid  as  hydrochloric  acid  or  nitric  acid. 
It  reacts,  however,  with  most  metals,  the  rapidity  of  the 
action  and  the  products  formed  depending  upon  the  tem- 
perature, the  metal,  and  the  amount  of  water  present. 


CHEMICAL  PROPERTIES  545 

Dilute  sulphuric  acid  gives  a  sulphate  and  hydrogen  with 
metals  like  iron  and  zinc  : 

Zn     +      H2S04     —  >-     ZnS04     +      H2 

zinc  sulphuric  acid  zinc  sulphate        hydrogen 

The  metals  mercury,  silver,  and  copper  are  practically 
unaffected  by  the  dilute  acid,  but  the  hot,  concentrated 
acid  reacts  with  them  so  as  to  produce  sulphur  dioxide 
instead  of  hydrogen  : 


Cu   +  2H2SO4—  ^CuSO4+  SO2  +  2  H2O 

copper        sulphuric  copper         sulphur         water 

acid  sulphate        dioxide 

One  explanation  for  this  action  is  that  the  excess  of  hot 
concentrated  acid  oxidizes  the  hydrogen  first  formed  by  the 
interaction  of  metal  and  acid  : 

Cu    +  H2SO4-^CuSO4  +    2H 

copper        sulphuric  copper  nascent 

acid  sulphate        hydrogen 

2  H  +  H2S04—  »-H20  4-    H2S03 

nascent          excess  water         sulphurous 

hydrogen         of  acid  acid 

The  sulphurous  acid  formed  breaks  down  in  the  hot  solution 
into  water  and  sulphur  dioxide  : 

H2S03  —  ->-H20  +      S02 

sulphurous  water  sulphur 

acid  dioxide 

Sulphuric  acid  has  a  powerful  dehydrating  action  on 
many  compounds,  by  taking  from  them  hydrogen  and 
oxygen  in  the  proportion  in  which  these  elements  combine 
to  form  water.  Thus  with  paper,  wood,  and  sugar,  the 
removal  of  the  hydrogen  and  oxygen  leaves  a  charred  mass 
of  carbon.  The  dehydrating  action  makes  sulphuric  acid 
burns  very  painful  and  dangerous.  Many  of  the  industrial 
uses  of  the  acid  depend  upon  its  dehydrating  action. 


546  COMMERCIAL   CHEMICALS 

490.  Uses.  —  Next  to  fertilizers,  sulphuric  acid  is  the 
chemical  product  of  greatest  value  in  this  country.     More 
than  one  hundred  and  fifty  manufacturing  plants  are  de- 
voted to  its  production.     By  far  the  greatest  quantity  of 
the  acid  is  used  in  the  preparation  of  fertilizers,  partic- 
ularly phosphates  and  ammonium  sulphate.     The  refining 
of  petroleum  consumes  the  next  largest  amount.     Other 
important   uses  are  the  pickling  of  iron  and  steel,  the 
preparation  of  sulphates,  particularly  aluminum  sulphate, 
and,  in  connection  with  nitric  acid,  the  manufacture  of 
explosives.     So  varied  are  the  uses  of  this  acid  that  there 
is  hardly  an  industry  that  does  not  depend  directly  or 
indirectly  upon  sulphuric  acid  or  some  product  made  with 
it. 

SULPHUR 

491.  Extraction.  — Sulphur  is  an  element  of  great  com- 
mercial value.     Formerly  the  chief  sources  of  native  or 
uncombined  sulphur  were  volcanic  regions,  particularly 
Sicily  and  Japan.     In  Sicily  the  rocky  material  contain- 
ing the  sulphur  is  heaped  into  piles,  which  are  covered  with 
spent  ore,  so  that  only  sufficient  air  is  admitted  to  burn  a 
small  portion  of  the  sulphur.     The  sulphur  that  burns 
produces  sufficient  heat  to  melt  the  remainder  of  the  sul- 
phur, which  runs  out  of  the  bottom  of  the  pile  into  a  col- 
lecting pool.     This  crude  sulphur  is  purified  by  remelting 
in  iron  pots  from  which  it  is  run  into  retorts,  where  it  is 
vaporized.     The  vapor  is  passed  into  brick  chambers,  where 
it  deposits  on  the  cool  walls  as  a  fine  powder,  known  as 
flowers  of  sulphur.     Soon,  however,  the  walls  become  warm 
and  most  of  the  vaporized  sulphur  condenses  as  a  liquid, 
which  makes  its  way  to  the  outlet  of  the  condensing  cham- 
ber.    It  is  then  cast  in  wooden  cylindrical  molds.     This 
form  is  roll  sulphur,  or  brimstone. 


EXTRACTION  OF  SULPHUR 


547 


The  sulphur  used  in  this  country  is  obtained  almost  en- 
tirely from  the  Louisiana  deposits.  These  beds  are  about 
500  feet  below  the  surface.  An  Austrian,  a  French,  and 
several  American  companies  failed  in  their  efforts  to  bring 
the  sulphur  to  the  surface  on  a  profitable  basis,  on  account 
of  quicksands  overlying  the  deposits.  It  remained  for 
Herman  Frasch,  long  distinguished  as  an  oil  chemist,  to 
solve  the  problem  in  a  most  ingenious  and  scientific  way. 


Copyright  by  The  Scientific  American. 

FIG.   1 75.  —  LOUISIANA  SULPHUR  WELL  WITH  ITS  BATTERY  OF  BOILERS. 

In  the  Frasch  process,  a  hole  is  bored  and  piped  down 
through  the  500  feet  of  overlying  deposits  to  the  bottom 
of  the  sulphur  bed,  which  is  200  feet  more.  Inside  the 
large  pipe  casing  of  the  hole  for  the  entire  distance  is  a 
6-inch  pipe,  and  inside  this  a  3-inch  pipe,  which  in  turn 
surrounds  a  1-inch  pipe  for  supplying  hot  compressed 
air.  Through  the  6-inch  pipe  water  heated  to  167°  C. 
under  a  pressure  of  100  Ibs.  is  forced  down  the  well  to 


548 


COMMERCIAL   CHEMICALS 


melt  the  sulphur  below.  '  The  hot,  compressed  air  mingles 
with  the  liquid  sulphur  and  so  reduces  the  specific  grav- 
ity of  the  liquid  to  be  raised  to  the  surface.  /  The  com- 
bined pressure  of  the  column  of  hot  water  and  hot  air 
raises  the  sulphur  to  the  surface  through  the  3-inch  pipe. 
Strainers  at  the  bottom  prevent  the  earthy  material  from 
being  driven  upward.  On  reaching  the  surface,  the 
melted  sulphur  is  run  into  huge  bins  60  feet  high,  made 
of  rough  boards.  The  sulphur  soon  cool^s,  forming  an 
enormous  block  of  solid  sulphur  of  remarkable  purity. 
Some  of  these  blocks  contain  100,000  tons  of  sulphur 
(Fig.  176).  The  block  is  broken  by  blasting  and  is  loaded 
on  cars  by  steam  shovels. 


Copyright  by  The  Scientific  American. 

FIG.   176.  —  BLOCK  OF  LOUISIANA  SULPHUR. 

As  the  sulphur  is  pumped  out,  the  overlying  clay  and 
sand  tend  to  follow  the  settling  of  the  sulphur  rock.  To 
prevent  the  breaking  of  the  well  pipes  by  the  resulting 
strains,  it  was  found  necessary  to  protect  them  by  casing 
the  hole  through  the  clay  with  a  12-inch  pipe  having  tele- 


AMMONIA  549 

scoping  joints.  The  sulphur  obtained  is  over  99  %  pure, 
and  not  only  supplies  the  American  market,  but  is  shipped 
to  Europe  as  well. 

492.  Uses  of  Sulphur.  —  Sulphur  is  used  as  a  source  of 
sulphur  dioxide,  to  be  employed  for  bleaching  and  disin- 
fecting.    Either  the  element,   the  monochloride   of   sul- 
phur, or  antimony  sulphide,  serves  for  the  hardening  (vul- 
canizing) of  rubber.     Sulphur  is  now  less   used  for  the 
manufacture  of  fireworks  and  gunpowder,  but  finds  an  in- 
creasing use  in  the  manufacture  of  carbon  disulphide  and 
dyestuffs. 

493.  Ammonia.  —  The  principal  source  of  the  ammonia 
of  commerce  is  the  ammoniacal  liquid  obtained  in  the  de- 
structive distillation  of  soft  coal*(Chap.  XXXII).     The 
improved  ovens  for  the  manufacture  of  coke  provide  for 
the  recovery  of  the  ammonia  liberated  in  the  process.   The 
increasing  demand,  however,  for  ammonium  salts  as  fertil- 
izers has  directed  attention  to  the  possibility  of  the  syn- 
thesis   of    ammonia    from    the    elements    nitrogen    and 
hydrogen: 

2N2     +     3H3     ^±      2NH? 

nitrogen  hydrogen  ammonia 

The  reaction  is  a  reversible  one,  and  the  small  yield  of 
ammonia  has  been  the  bar  to  its  development  on  a  com- 
mercial scale. 

It  has  been  found,  however,  that  by  the  use  of  a  suitable 
catalytic  agent  and  the  regulation  of  temperature  and 
pressure,  synthetic  ammonia  can  be  made  profitably.  Iron 
and  uranium  are  among  the  metals  used  as  catalyzers.  The 
best  temperature  range  is  between  500°  C.  and  700°  C.  and 
the  pressure  from  100  to  200  atmospheres.  A  mixture  of 
1  volume  of  nitrogen  with  3  of  hydrogen  is  passed  over 


550  COMMERCIAL    CHEMICALS 

the  catalytic  agent  in  a  furnace  of  special  design.  Then 
the  hot  gases  are  subjected  to  a  low  temperature,  so  as  to 
liquefy  the  ammonia  formed  and  to  separate  it  from  the 
nitrogen  and  hydrogen  remaining  uncombined. 

Ammonia  is  sold  in  its  water  solution.  The  concen- 
trated commercial  article  has  a  specific  gravity  of  about 
0.9  and  contains  almost  30%  of  the  gas  (NH3).  This 
water  solution  contains  some  of  the  ammonia  in  the  form 
of  ammonium  hydroxide,  but  the  larger  portion  is  in  phys- 
ical solution.  Household  ammonia  is  supposed  to  contain 
8  %  NH3,  but  the  commercial  article  sometimes  contains 
as  low  as  2  %  of  ammonia. 

Ammonium  hydroxide  is  an  active  alkali  and,  like 
sodium  hydroxide,  acts  slowly  upon  glass.  This  accounts 
for  the  opaque -appearance  of  the  reagent  bottles  used  for 
ammonium  hydroxide  in  the  laboratory. 

Liquefied  ammonia  is  the  gas  (NH3)  which  has  been  re- 
duced to  a  liquid  by  pressure.  It  is  important. in  the 
manufacture  of  artificial  ice  and  for  use  in  refrigerating 
plants.  In  the  latter,  the  cooling  liquid  circulating  in  the 
pipes  is  brine,  which  has  been  cooled  by  the  evaporation  of 
liquid  ammonia. 

494.  Sodium  and  Potassium  Carbonates. — These  carbon- 
ates are  made  by  the  Solvay  process,  which  is  remarkable 
for  the  cheapness  and  efficiency  of  its  operation.  It  is 
based  on  the  reaction  between  sodium  chloride  and 
ammonium  bicarbonate  in  cold  solution.  Ammonium 
bicarbonate  may  be  made  by  the  following  reaction: 

NH3  +  H2O  +   CO2         — >-  NH4HCO3 

ammonia        water          carbon  ammonium 

dioxide  bicarbonate 

The  reaction  for  the  double  replacement  of  this  com- 
pound with  sodium  chloride  is : 


THE   SOLVAY  PROCESS  551 

NaCl  +  NH4HCO3  — ^  NaHCO3  +  NH4C1 

sodium          ammonium  sodium  ammonium 

chloride        bicarbonate  bicarbonate        chloride 

In  the  Solvay  process,  these  reactions  are  not  conducted 
in  just  this  way,  but  they  probably  take  place.  A  concen- 
trated brine  solution  is  saturated  with  ammonia  gas  in 
tanks  with  perforated  false  bottoms.  This  ammoiiiacal 
brine  is  pumped  under  pressure  to  a  carbonating  tower, 
which  is  about  70  feet  high.  The  brine  enters  the  tower 
about  halfway  up  and  flows  down  in  a  circuitous  course, 
meeting  carbon  dioxide,  which  comes  into  the  bottom  of 
the  tower  under  pressure.  The  carbon  dioxide  expands 
as  it  rises  through  the  tower,  and  consequently  produces  a 
cooling  effect.  This  and  other  cooling  devices  counter- 
balance the  heat  developed  by  the  reaction,  and  establish 
the  most  desirable  temperature  (30°  C.  to  35°  C.)  for  the 
absorption  of  the  carbon  dioxide  by  the  ammoniacal  brine. 

The  sodium  bicarbonate,  precipitated  under  the  existing 
solubility  conditions,  is  drawn  off,  filtered,  and  washed. 
The  bicarbonate  is  then  heated  in  iron  pans: 

2NaHCO8— >-NaaCO8  +  H2O  +  CO2 

sodium  sodium  water       carbon 

bicarbonate  carbonate  dioxide 

The  sodium  carbonate  thus  obtained  is  nearly  pure.  Pure 
bicarbonate  is  obtained  from  it  by  passing  carbon  dioxide 
into  a  solution  of  the  carbonate  : 

Na2CO3  +  H2O  +  CO2  —^2  NaHCO3 

sodium  water        carbon  sodium 

carbonate  dioxide  bicarbonate 

The  process  serves  equally  well  for  the  production  of 
potassium  bicarbonate  and  of  potassium  carbonate. 

495.  Economy  of  the  Solvay  Process.  —  The  carbon  dioxide 
liberated  in  the  conversion  of  the  bicarbonate  into  the  car- 


552 


COMMERCIAL    CHEMICALS 


bonate  is  used  in  the  carbonating  tower.  Ammonium  chlo- 
ride is  recovered  from  the  water  of  the  tower  solution  and 
heated  with  quicklime  to  regenerate  the  ammonia  gas  for 
another  cycle  of  operations.  Quicklime  is  obtained  by 
heating  limestone.  During  this  process  carbon  dioxide  is 
evolved  and  is  used  in  the  carbonating  tower.  Thus, 
after  the  process  once  starts,  the  principal  cost  of  materials 
is  for  the  water,  salt,  and  limestone.  Small  quantities  of 
an  ammonium  salt  have  to  be  purchased  from  time  to  time 
to  replenish  the  slight,  but  unavoidable,  loss  of  ammonia. 

496.  Sodium  Hydroxide.  —  In  order  to  meet  the  enormous 
demand  for  caustic  soda  (sodium  hydroxide,  NaOH)  a  num- 
ber of  processes  for  preparing  it  have  been  devised.  The 
most  efficient  of  these  is  the  Castner  process,  which  is 
based  upon  the  following  reaction  for  the  electrolysis  of, 
brine: 


2NaCl 

sodium  chloride 


2H2O 

water 


>-   2  NaOH    +    C12    +    H2 

sodium  hydroxide    chlorine    hydrogen 


The  chief  practical  problem  in  the  electrolysis  of  sodium 
chloride  is  to  keep  the  chlorine  from  reacting  with  either 

the     sodium     hydroxide 

6.  sfllfl'      A         t  an    .  or  the    liberated   hydro- 

gen. The  reaction  with 
hydrogen  would  probably 
be  explosive.  In  the 
Castner  process,  the  elec- 
trolysis is  carried  on  in  a 
stone  box,  divided  into 

three  compartments  (Fig.  177)  by  vertical  partitions  reach- 
ing nearly  to  the  bottom.  Brine  is  run  into  the  two  end^ 
compartments  and  pure  water  into  the  middle  one.  On 
the  bottom  of  the  tank  is  a  thin  layer  of  mercury,  into 


FIG.  177.  —  CASTNER  CELL. 


SODIUM  HYDROXIDE  553 

which  the  partitions  dip,  in  order  to  prevent  the  mixing 
of  the  liquids  in  the  end  compartments  with  the  liquid 
in  the  middle. 

Several  T-shaped  anodes  of  Acheson  graphite  are 
suspended  in  each  brine  compartment.  The  layer  of  mer- 
cury is  negative  relative  to  the  anode  and  positive  relative 
to  the  cathode.  The  current,  entering  at  the  anode,  passes 
through  the  brine  to  the  mercury  ;  the  sodium  moves  with 
the  current,  while  the  chlorine  is  attracted  to  the  anode: 

NaCl     — ^    Na     +     Cl 

sodium  chloride          sodium          chlorine 

The  sodium  is  first  liberated  in  contact  with  the  mercury 
and  amalgamates  with  it,  the  amalgam  floating  on  the 
surface.  An  eccentric  tilts  the  cell  up  and  down  at  half- 
minute  intervals.  As  the  cell  is  inclined,  the  amalgam 
flows  into  the  center  compartment,  which  contains  a  weak 
solution  of  sodium  hydroxide  at  the  beginning  of  the 
process.  The  sodium  continues  to  migrate  with  the  cur- 
rent through  the  center  compartment,  leaves  the  mercury, 
and  is  finally  liberated  at  the  cathode.  Here  it  reacts  with 
water,  forming  sodium  hydroxide  : 

2Na    +    2H2O   — *-   2NaOH    +    H2 

sodium  water  sodium  hydroxide    hydrogen 

As  soon  as  the  caustic  soda  solution  has  reached  a 
specific  gravity  of  1.3,  its  concentration  is  kept  constant 
by  continuously  drawing  off  a  portion  of  the  liquid  and 
replacing  it  with  a  stream  of  fresh  water.  The  solution  is 
then  evaporated  in  iron  pots  to  drive  off  the  water,  and 
the  caustic  soda  is  either  cast  into  sticks  or  run  into  iron 
drums. 

The  brine  in  the  end  compartments  is  kept  circulating 
and  salt  is  put  in  to  keep  its  concentration  constant. 


554  COMMERCIAL    CHEMICALS 

The  chlorine  liberated  at  the  anode  is  led  off  through 
pipes  and  is  used  in  making  bleaching  powder.  The  hy- 
drogen is  usually  a  waste  product.  The  mercury  not  only 
acts  as  a  seal  between  the  compartments,  but  it  conducts 
the  current  from  the  end  compartments  to  the  middle. 

By  using  a  solution  of  potassium  chloride  instead  of 
sodium  chloride,  the  electrolytic  process  serves  equally 
well  for  the  manufacture  of  caustic  potash,  potassium 
hydroxide. 

497.  Hypochlorites.  —  Although  chlorine  is  sold  liquefied 
in  steel  cylinders,  most  of  the  chlorine  for  industrial  uses 
is  shipped  in  the  form  of  hypochlorites.  These  powerful 
oxidizing  and  bleaching  agents  are  salts  of  hypochlorous 
acid,  HC1O.  There  are  several  electrolytic  processes  for 
making  hypochlorites. 

When  chlorine  is  passed  into  a  cold  solution  of  a  caustic 
alkali,  as  sodium  hydroxide,  the  following  reaction  occurs  : 

2NaOH    +    Cla  — ^  NaClO    +    NaCl   +    H2O 

sodium  chlorine  sodium  sodium  water 

hydroxide  hypochlorite          chloride 

Sodium  hypochlorite  is  used  in  its  water  solution  under 
the  name  of  Javelle  water. 

Calcium  hypochlorite  is  made  in  a  similar  manner  by 
passing  chlorine  gas  into  milk  of  lime  : 

2  Ca(OH)2  +  2  C12  -H>-  Ca(ClO)2  +  CaCl2  +  2  H2O 

calcium  chlorine  calcium  calcium          water 

hydroxide  hypochlorite          chloride 

The  conditions  for  the  reaction  are  an  excess  of  lime  and 
a  temperature  below  33°  C.  The  water  solution  of  calcium 
hypochlorite  made  in  this  way  is  much  used  as  a  bleaching 
liquor.  On  account  of  its  bulk  it  is  not  transported,  but 
is  made  where  it  is  to  be  used. 


CHLORA  TES  555 

498.  Bleaching  Powder.  -  -  The  compound  containing 
available  chlorine  which  can  be  profitably  shipped  is 
bleaching  powder,  a  compound  similar  in  composition  to 
calcium  hypochlorite.  Chemists  are  not  agreed  as  to  the 
correct  formula  for  bleaching  powder,  but  it  is  often 
represented  by  CaOCl2. 

Bleaching  powder  is  made  by  passing  chlorine  through 
a  series  of  chambers  containing  slaked  lime,  spread  in  a 
thin  layer  on  the  floor  or.  on  shelves.  The  powder  is 
shipped  in  tight  containers,  as  moist  air  rapidly  decom- 
poses it.  Bleaching  powder  yields  chlorine  when  treated 
with  dilute  acids,  even  as  weak  as  carbonic  acid. 

Upon  the  reaction  with  an  acid  depends  the  use  of 
bleaching  powder  as  a  source  of  chlorine  for  bleaching 
cotton,  linen,  and  other  materials.  Its  use  as  a  disinfec- 
tant, "  chloride  of  lime,"  is  due  to  the  slow  liberation  of 
chlorine  by  moist  air  containing  carbon  dioxide.  It  is 
well  to  recall  that  both  the  bleaching  and  disinfecting 
action  of  chlorine  depends  in  a  large  measure  on  the 
reaction : 

Cla     +     H20  — »-         2  HC1         +          O 

chlorine  water  hydrochloric  acid        nascent  oxygen 

The  active  agent  of  bleaching  powder  is  believed  to  be 
nascent  oxygen. 


499.  Chlorates.  —  Potassium  chlorate  is  made  by  the 
electrolysis  of  a  warm  concentrated  solution  of  potassium 
chloride.  The  initial  products  of  the  electrolysis,  namely, 
chlorine  and  potassium  hydroxide,  are  brought  together 
by  stirring,  and  react,  finally  producing  the  chlorate  : 


6KOH     +     3C12    — >-     KC1O3     +     5  KC1    +   3  H2O 

potassium  chlorine  potassium  potassium  water 

hydroxide  chlorate  chloride 


556  COMMERCIAL   CHEMICALS 

On  cooling  the  solution,  the  potassium  chlorate  crystal- 
lizes out,  and  the  remaining  potassium  chloride  solution 
is  again  electrolyzed. 

Potassium  chlorate  is  the  only  chlorate  of  commercial 
importance.  It  is  used  in  the  manufacture  of  dyes  and 
in  making  oxygen  gas.  The  potash  tablets  used  for  sore 
throats  are  composed  of  this  compound. 

500.  Hydrogen  Peroxide. — This  compound  is  prepared 
by  the  action  of  barium  peroxide  with  a  dilute  acid  (sul- 
phuric or  phosphoric).  The  barium  peroxide  is  mixed 
with  water  to  the  consistency  of  cream.  This  mixture  is 
then  added  to  a  dilute  solution  of  phosphoric  acid,  care 
being  taken  to  keep  the  temperature  below  15°  C.  : 

3  BaO2  +   2  H3PO4    — +-  Ba3(PO4)2  +  3  H2O2 

barium  phosphoric  barium  hydrogen 

peroxide  acid  phosphate  peroxide 

The  precipitate  of  barium  phosphate  is  allowed  to  settle 
and  the  solution  of  hydrogen  peroxide  drawn  off. 

The  commercial  form  of  hydrogen  peroxide  is  its  3  % 
water  solution.  To  prevent  the  peroxide  from  decomposi- 
tion, the  solution  is  kept  slightly  acid  or  a  very  small 
quantity  of  acetanilid  is  added.  It  is  sold  under  various 
trade  names,  such  as ."  Dioxogen  "  and  "Aerozone." 

Hydrogen  peroxide  is  a  clear,  sirupy  liquid  about  1.5 
times  as  dense  as  water.  Concentrated  hydrogen  peroxide 
is  likely  to  decompose  with  explosive  violence.  Even  in 
the  dilute  3  %  water  solution,  the  decomposition  proceeds 
slowly  according  to  the  equation  : 

H202          ^±l  H20  +          O 

hydrogen  peroxide  water        nascent  oxygen 

Upon  the  activity  of  the  nascent  oxygen  depend  the 
uses  of  "  peroxide  "  as  a  disinfecting  and  bleaching  agent. 


SODIUM   PEROXIDE  557 

Harmful  bacteria  and  decomposing  organic  matter  are 
destroyed  by  it,  hence  its  use  as  an  antiseptic  for  super- 
ficial wounds  and  sores.  It  has  very  little  action  on  liv- 
ing tissue,  and  the  water  formed  in  its  decomposition  does 
not  give  rise  to  further  irritation,  as  do  many  other  disin- 
fectants. Silk,  feathers,  hair,  and  ivory  are-  bleached  by 
the  oxidation  of  their  coloring  matters. 

Some  physicians  object  to  the  use  of  hydrogen  peroxide 
for  some  purposes  on  account  of  the  small  amount  of  acid 
that  it  may  contain.  On  this  account,  hydrogen  peroxide 
should  be  mixed  with  limewater  when  used  as  a  gargle. 

501.  Sodium  Peroxide. —  This  compound  is  made  by  heat- 
ing slices  of  sodium  in  air  freed  from  carbon  dioxide  : 

2  Na  +     O2      — »-     Na2O2 

sodium        oxygen  sodium  peroxide 

The  temperature  for  the  reaction  must  be  kept  between 
300°  C.  and  400°  C. 

Sodium  peroxide  reacts  violentty  with  water,  producing 
sodium  hydroxide  and  oxygen  : 

2Na202    +     2H20     — ^     4  NaOH       +       O2 

sodium  peroxide  water  sodium  hydroxide  oxygen 

When  the  reaction  is  carefully  regulated,  it  is  a  most  con- 
venient laboratory  method  for  making  small  quantities  of 
oxygen.  Sodium  peroxide  should  never  be  left  on  paper  or 
other  combustible  material,  as  the  heat  of  reaction  with 
moisture  may  cause  a  blaze.  Sodium  peroxide  is  useful  for 
making  solutions  of  hydrogen  peroxide  for  laboratory  use, 
by  sifting  it  into  dilute  acid  solutions  : 

Na2O2       +       2  HC1     — >-     H2O2        +        2  NaCl 

sodium  peroxide      hydrochloric  acid      hydrogen  peroxide      sodium  chloride 

The  use  of  sodium  peroxide  as  an  oxidizing  and  bleaching 
agent  is  increasing. 


558  COMMERCIAL    CHEMICALS 

SOME   IMPORTANT  COMMERCIAL   SALTS1 


SCIENTIFIC  NAME 

COMMON  NAME 

FORMULA 

IMPORTANT  USES 

Ammonium       sul- 

(NH4)2S04 

Fertilizer;      fire- 

phate 

proofing  fabrics 

Aluminum  sulphate 

A12(S04)3 

Water     purifica- 
tion 

Calcium  sulphate 

Plaster        of 

2CaSO4.  H2O 

Molds  and  casts 

Paris 

FeiTous  sulphate 

Green  vitriol 

FeSO4.  7  H2O 

Inks 

Lead  acetate 

Sugar  of  lead    Pb(C2H3O2)2 

Making  pigments 

T*r\-j-oo  ain  TVI    r*\ro  n  irJt* 

irnxT 

T7«        ,                 ,.                                     . 

-EjXtrac  tion        or 
gold 

Potassium    dichro- 

K2Cr2O7 

Chrome  tanning 

mate 

Potassium  ferrocy- 

Yellow     prus- 

K4Fe(CN)e 

Making  pig- 

anide 

siate  of  pot- 

ments, e.g. 

ash 

Prussian  blue 

Potassium  perman- 

  i_ 

KMuO4 

Oxidizing  agent  ; 

ganate 

germicide 

Sodium  bicarbonate 

Baking  soda 

NaHC03 

Constituent       of 

baking  powders 

Sodium  silicate 

Water  glass 

Na2Si03 

Protective    coat- 

ings ;         calico 

printing  ;     spe- 

cial cements  _ 

Sodium  tetraborate 

Borax 

Na2B4O7.10H2O 

Soldering;  soaps 

Sodium        thiosul- 

Hypo 

Na2S2O3  .  5  H2O 

Photography 

phate 

Tin  chloride 

Tin  salt 

SnCl2.2H2O 

Dyeing;   weight- 

ing silk 

1  Other  common  salts  will  be  found  in  the  table  on  page  41. 


SUMMARY  559 

SUMMARY 

Grades  of  Commercial  Chemicals  are  crude,  technical,  C.  P., 
and  analyzed. 

Hydrochloric  Acid  is  made  by  heating  salt  with  concentrated 
sulphuric  acid.  Hydrochloric  acid  is  an  active  acid,  yielding 
hydrogen  and  a  chloride  with  most  metals,  except  the  noble 
metals  and  those  with  insoluble  chlorides.  It  has  a  wide  range 
of  industrial  uses. 

Nitric  Acid  is  made  by  heating  sodium  nitrate  with  sulphuric 
acid.  Nitric  acid  reacts  with  most  metals,  forming  nitrates  and 
a  gaseous  product,  which  is  almost  invariably  a  reduction  product, 
e.g.,  nitric  oxide  or  nitric  peroxide.  This  is  due  to  the  readi- 
ness of  nitric  acid  to  give  up  oxygen.  Easily  oxidizable  materials 
are  attacked  vigorously  by  nitric  acid.  Nitric  acid  is  used  in  the 
manufacture  of  nitroglycerine,  nitrocellulose  products,  and  dye- 
stuffs.  Its  salts  have  many  important  applications. 

Sulphuric  Acid  is  made  by  both  the  contact  and  the  cham- 
ber processes.  These  are  alike  in  that  sulphur  dioxide  is  first 
formed  and  then  oxidized  to  sulphur  trioxide,  which  is  taken  up 
by  water.  Sulphuric  acid  is  a  heavy,  oily  liquid,  but  is  not  so 
active  as  hydrochloric  or  nitric  acid.  The  dilute  acid  yields 
hydrogen  and  a  sulphate  with  the  metals  iron  and  zinc.  The  hot 
concentrated  acid,  with  the  metals  copper  and  mercury,  gives 
sulphur  dioxide  as  a  gaseous  product,  on  account  of  the  oxidizing 
action  of  the  excess  of  sulphuric  acid.  Another  important  action 
of  sulphuric  acid  is  its  dehydrating  power,  as  many  uses  are 
based  upon  it.  There  is  hardly  an  important  industry  which  does 
not  depend  directly  or  indirectly  on  some  use  of  this  acid. 

Sulphur  is  obtained  from  Louisiana,  Sicily,  Hawaii,  and  Japan. 
The  commercial  forms  are  flowers  of  sulphur  and  brimstone. 

Ammonia  is  a  by-product  obtained  in  the  destructive  distilla- 
tion of  soft  coal.  Ammonia  in  water  solution  gives  a  cheap  and 
very  useful  base.  Liquid  ammonia  is  used  in  ice-making  and  in 
refrigerating  plants. 


560  COMMERCIAL    CHEMICALS 

Sodium  and  Potassium  Carbonates  are  made  by  the  Solvay 
process,  one  of  the  first  chemical  processes  to  become  highly 
efficient. 

Sodium  and  Potassium  Hydroxides  are  made  by  the  Castner 
process,  in  which  a  solution  of  brine  is  electrolyzed. 

Bleaching  Powder  is  made  by  the  reaction  of  chlorine  with 
lime,  and  is  used  for  bleaching  and  disinfecting. 

Potassium  Chlorate  is  made  by  the  electrolysis  of  a  solution  of 
potassium  chloride. 

Hydrogen  Peroxide  is  made  by  the  reaction  of  a  dilute  acid 
with  barium  peroxide.  The  commercial  article  is  a  3%  water 
solution  used  for  bleaching  and  disinfecting. 

EXERCISES 

1.  Why  do  chemist^  prefer  analyzed  chemicals  to  the  C.  P. 
grade  for  their  analytical  operations  ? 

2.  Show  how  the  solubility  of  hydrogen  chloride  is  utilized 
in  the  manufacture  of  hydrochloric  acid. 

3.  Why  does  a  bottle   of   concentrated   hydrochloric   acid 
fume  when  opened  to  the  air  ? 

4.  Why  is  hydrochloric  acid  inactive  with  lead  and  silver  ? 
How  does  it  act  with  zinc  and  iron  ? 

5.  Write  the  equation  for  the  reaction  of  hydrochloric  acid 
with  a  carbonate.     With  a  sulphide. 

6.  Why  is  concentrated  sulphuric  acid  used  in  preparing 
both  hydrochloric  and  nitric  acids? 

7.  Why   should   not   bottles   of   nitric   acid  be   stored   on 
wooden  shelves? 

8.  Name  three  chemicals  that  should  not  be  placed  near 
concentrated  nitric  acid  in  a  chemical  stock  room. 

9.  How  could  you  determine  whether  a  ring  were  brass  or 
gold? 


EXERCISES  .  561 

10.  Explain  why  we  do  not  get  hydrogen  as  the  gaseous 
product  when  copper  reacts  with  concentrated  nitric  acid. 

11.  Why  will  a  gas  flame  burn  in  the  hot  vapor  of  nitric 
acid? 

12.  Give  the  modern  chemical  name  for  each  of  the*  follow- 
ing acids :  muriatic  acid,  oil  of  vitriol,  and  aqua  *fortis. 

13.  What  difficulties  arose  in  the  commercial  preparation  of 
sulphur  trioxide  ? 

14.  What   grade   of   acid   is   best    made    by    the    contact 
process  ?     By  the  chamber  process  ? 

15.  Which  contains  less  water,  concentrated  hydrochloric 
acid  or  concentrated  sulphuric  acid?     Explain. 

•  16.    Account  for  the  production  of  sulphur  dioxide   when 
sulphuric  acid  reacts  with  certain  metals. 

17.  Write   an   equation   for   a    laboratory   preparation    of 
hydrogen  when  sulphuric  acid  is  used. 

18.  Why   is   concentrated   sulphuric  acid  used  in  making 
nitroglycerine  ? 

19.  Of  what  advantage  is  the  low  melting  point  of  sulphur 
in  the  Louisiana  method  of  extraction  ? 

20.  What   stimulus  led  to  the   development   of   electrical 
methods  for  manufacturing  ammonia  and  nitrates? 

21.  Why  was  the  price  of  soda  lowered  when  the  Solvay 
process  was  established  ? 

22.  Why   is   electrolytic  caustic  soda  comparatively  pure 
and  cheap? 

23.  Why  can  chloride  of  lime  be  used  as  a  disinfectant  ? 

24.  Why  is  bleaching  powder  priced  according  to  the  avail- 
able amount  of  chlorine  that  it  contains  ? 

25.  How  is  hydrogen  peroxide  serviceable  to  dentists  ? 

26.  Why  is  the  household  ammonia  of  bargain  sales   not 
necessarily  cheap  ? 


CHAPTER   XLV 

AGRICULTURE 

502.  Fertility  of  the  Soil. — In  the  United  States,  it  has 
been  customary  to  farm  for  the  profit  of  the  present  gen- 
eration, with  little  thought  of  those  who  were  to  follow. 
When  the  fertility  of  a  farm  became  so  low  that  agricul- 
ture was  no  longer  profitable,  the  farm    was   frequently 
abandoned  and  those  who  wished  to  engage  in  agriculture 
sought  virgin  soil  in  other  parts  of  the  country.     The  re- 
sult, as  seen  to-day,  is  that  there  are  in  the  East  hun- 
dreds of  abandoned  farms,  and  many  soils  of  the  Middle 
West,    once    considered    inexhaustible,    have   greatly   de- 
creased in  fertility. 

At  present,  our  more  intelligent  citizens  are  beginning 
to  realize  that  little  virgin  soil  exists  in  the  United  States, 
and  that  food  must  be  furnished  for  a  rapidly  increasing 
population.  The  increased  cost  of  living  is  causing  much 
serious  thought  concerning  the  supply  and  demand  of 
food.  The  restoration  of  fertility  to  worn-out  farms  is  a 
problem  that,  sooner  or  later,  must  be  solved  if  the  coun- 
try is  to  prosper.  A  fertile  soil  is  necessary  not  only  to 
the  production  of  food  for  this  growing  nation,  but  for 
the  production  of  over  four  fifths  of  all  of  the  raw  mate- 
rial used  in  our  manufactures  as  well. 

503.  Elements  Essential  to  Plant  Life.  —  Let  us  consider 
some  of  the  fundamental  principles  involved  in  the  prob- 
lem  of  increasing  the  fertility  of  farm  lands.     The  ele- 
ments   hydrogen,  carbon,   oxygen,  nitrogen,    phosphorus, 

562 


ELEMENTS  ESSENTIAL   TO  PLANT  LIFE       563 

potassium,  sulphur,  magnesium,  calcium,  and  iron  are  ab- 
oolutely  essential  to  plant  life.     If  any  one  of  them  is 


FIG.  178.  —  STAPLE  CROPS  :    CORN. 


lacking,  no  plant  life  can  exist.  In  addition  to  these  ele- 
ments, silicon,  chlorine,  and  sodium  are  necessary  to  the 
full  development  of  many  plants. 


564 


AGRICULTURE 


Of  the  ten  essential  elements,  carbon  is  derived  from 
the  carbon  dioxide  of  the  air ;  oxygen  from  air  and  water  ; 
hydrogen  is  derived  from  water.  In  few  instances  can 

nitrogen  be  taken  from  the 
air  —  never  directly  by  flow- 
ering plants.  This  leaves 
six  elements  which  farm 
crops  always  take  from  the 
soil.  Nitrogen,  phosphorus, 
and  potassium  frequently  be- 
come diminished  to  such  an 
extent  that  the  soil  fails  to 
yield  a  profitable  crop.  For 
this  reason  nitrogen,  phos- 
phorus, and  potassium 
compounds  constitute  the 
essential  ingredients  of  com- 
mercial fertilizers.  In  ad- 
dition to  such  compounds,  it 
becomes  necessary  in  some 
instances  to  add  compounds  containing  calcium,  mag- 
nesium, and  sulphur.  Elements  taken  from  the  soil  in 
large  quantities  by  crops  must  be  returned  to  it  in  the 
form  of  suitable  compounds,  if  the  soil  is  not  to  decrease 
in  fertility.  Man  cannot  hope  to  have  something  made 
from  nothing. 

In  the  illustration  (Fig.  179)  is  shown  the  effect  of 
various  elements  on  the  growth  of  barley  in  water,  viz. : 
(1)  Complete  manure ;  (2)  No  nitrogen ;  (3)  No  phos- 
phoric acid ;  (4)  No  potash ;  (5)  No  lime ;  (6)  No  mag- 
nesia. 


123456 

Copyright  by  The  Scientific  American. 

FIG.  179. — WATER  CULTURES  OF 
BARLEY. 


504.   Soils.  —  Before  the  application  of  commercial  fer- 
tilizers to  the  soil  can  be  made  intelligently,  the  composi- 


SOILS  565 

tion  of  the  soil  must  be  studied.  Soils  are  formed  by  the 
disintegration  of  rocks  and  by  the  accumulation  of  de- 
cayed organic  matter.  They  may  be  deposited  over,  or 
near,  the  rocks  from  which  they  are  derived,  or  may  be 
transported  many  miles  from  the  place  of  their  origin. 
To-day  water  is  the  great  transporting  agent,  but  in  the 
past  enormous  masses  of  rock  and  earth  were  brought 
from  Canada  by  glaciers  and  deposited  over  the  northern 
portion  of  the  United  States.  A  study  of  the  native  rock 
near  a  field  will  sometimes  aid  in  determining  the  ele- 
ments likely  to  be  lacking  in  the  soil. 

The  disintegration  of  feldspathic  rocks  results  in  the 
formation  of  clay  soils.  As  the  most  common  variety  of 
feldspar  is  a  silicate  of  potassium  and  aluminum,  such  a 
soil  is  not  likely  to  be  deficient  in  potassium.  On  the 
other  hand,  the  disintegration  of  limestone  yields  a  soil 
very  likely  to  be  deficient  in  that  element.  On  account 
of  the  large  number  of  fossils  frequently  found  in  lime- 
stone, a  soil  derived  from  it  may  be  rich  in  phosphorus 
compounds.  Loam  is  a  mixture  of  sand  with  vegetable 
matter  and  frequently  clay.  Sandy  soils  are  made  up 
largely  of  particles  of  silica.  They  have  a  coarser  struc- 
ture than  clay  or  lime  soils,  are  "  warmer "  and  more 
readily  aerated,  but  less  retentive  of  nitrogen  and  potas- 
sium compounds.  Rains  soon  carry  such  compounds  be- 
yond the  reach  of  plant  roots,  but  a  considerable  portion 
of  the  material  thus  removed  is  returned  to  the  plant  by 
the  capillarity  of  the  soil. 

The  ground  waters  of  clay  soils  carry  in  suspension 
minute  particles  of  clay.  On  the  evaporation  of  the 
water,  these  particles  are  deposited  in  a  hard  mass  which 
forms  an  impervious  layer  on  the  surface  of  the  soil. 
While  the  normal  capillarity  of  a  soil  containing  a  large 
proportion  of  clay  exceeds  that  of  a  sandy  soil,  the  order 


566  AGRICULTURE 

may  be  reversed  in  dry  weather  on  account  of  the  "  bak- 
ing "  of  the  surface  of  the  clay  soil. 

The  composition  of  the  soil  can  be  determined  by  the 
analysis  of  carefully  selected  samples,  but  this  is  work  for 
a  trained  chemist  and  not  for  the  student  of  elementary 


FIG.  180. — STAPLE  CROPS:    OATS. 

chemistry.  The  latter  may,  however,  be  able  to  deter- 
mine, by  the  experimental  application  of  fertilizers  and  by 
the  growth  of  plants  in  a  systematic  manner,  the  elements 
in  which  a  soil  is  deficient. 

505.  Reserve  Material.  —  There  may  be  present  in  a  soil 
a  supply  of  all  the  elements  necessary  to  plant  life  and  yet 
the  soil  may  be  unproductive  because  the  elements  are  con- 
tained in  compounds  which  plants  are  unable  to  decompose 
readily.  These  combined  elements,  not  directly  available 
for  plant  food,  constitute  the  reserve  material  of  the  soil. 
This  reserve  material  is  slowly  converted  into  available 


SOURCES   OF  NITROGEN  567 

compounds   by   the    action   of    the    atmosphere,    organic 
matter,  and  certain  inorganic  substances. 

506.  Amendments.  —  A  substance  added  to  the  soil,  not 
because  of  the  plant  food  it  contains,  but  on  account  of 
the  power  it  has  to  aid  in  the  liberation  of  plant  food  from 
compounds  containing  it  in  unavailable  forms,  is  called  an 
amendment.     Amendments  convert  the  unavailable  plant 
food  into  forms  that  can  be  assimilated  by  plants.     Lime 
and  ground  gypsum  are  the  amendments  most  frequently 
employed.     Stable  manure  is  sometimes  of  as  much  value 
as  an  amendment  as  for  the  plant  food  it  contains. 

SOURCES   OF  NITROGEN 

The  chief  materials  used  for  increasing  the  combined 
nitrogen  of  the  soil  are  sodium  nitrate,  ammonium  sul- 
phate, calcium  cyanamid,  and  various  organic  substances 
such  as  ground  dried  fish  scrap,  stable  manure,  guano, 
dried  blood,  cottonseed  meal,  and  ground  leather,  hoofs, 
horns,  and  hair. 

507.  Sodium  Nitrate,  or  Chili  saltpeter,  is  obtained  from 
extensive   deposits    along   the    western    coast    of    South 
America.     It  is  soluble  in  water,  and  the  nitrogen  it  con- 
tains is  readily  assimilated  by  plants  ;  6  pounds  of  pure 
sodium  nitrate  contain  about  1  pound  of  nitrogen.     The 
commercial  article  seldom  contains  more  than  95  %  of  that 
amount. 

508.  Ammonium  Sulphate  is  a  by-product  of  the  coal  gas 
works.     It  contains  nitrogen  in  a  form  slightly  less  avail- 
able for  plant  food  than  sodium  nitrate  ;  4.7  pounds  of 
pure  ammonium  sulphate  contain  1  pound  of  nitrogen. 

509.  Calcium   Cyanamid,   "  Cyanamid,"     or   "  lime-nitro- 
gen," is  of  more  than  ordinary  interest,  as  the  method  by 


568  A  GRIC  UL  TURK 

which  it  is  made  illustrates  one  of  the  modern  methods 
employed  for  the  fixation  of  nitrogen,  that  is,  for  the  con- 
version of  the  free  nitrogen  of  the  air  into  useful  com- 
pounds. The  reaction  employed  in  the  manufacture  of 
"  Cyanamid  "  was  discovered  in  1895.  Calcium  carbide, 
extensively  employed  in  the  manufacture  of  acetylene  gas, 
is  made  by  heating,  in  an  electric  furnace,  a  mixture  of 
calcium  oxide  and  coke  to  a  temperature  of  about  3500°  C, 


CaO   +   3C— >-CaC2    +   CO 

calcium        carbon         calcium          carbon 
oxide  carbide         monoxide 

The  calcium  carbide  thus  prepared  is  cooled,  crushed, 
heated  to  redness,  and  brought  in  contact  with  nitrogen, 
obtained  from  air.  An  impure  calcium  cyanamid  results  : 


CaC2   +N2— ^CN.NCa  +     C 

calcium     nitrogen  calcium  carbon 

carbide  cyanamid 

The  product  thus  obtained  is  further  treated  to  remove 
carbides,  phosphides,  and  sulphides,  which,  when  brought 
in  contact  with  the  soil,  would  produce  gases  injurious  to 
plant  life. 

The  use  of  "  Cyanamid  "  as  a  trade  name  is  unfortunate, 
as  the  term  really  belongs  to  the  chemical  compound 
CN  .  NH2  of  which  calcium  cyanamid,  CN  .  NCa,  may  be 
considered  a  salt. 

Commercial  "  Cyanamid  "  varies  in  composition,  but  is 
made  up  chiefly  of  calcium  cyanamid  mixed  with  various 
substances  such  as  calcium  hydroxide,  carbon,  calcium 
nitrate,  etc.  The  manufacturers  state  that  it  contains 
from  18 J  %  to  20  %  of  ammonia,  by  which  they  mean  that 
it  contains  nitrogen  sufficient  to  yield  from  18J%  to  20% 
of  ammonia. 

The  nitrogen  of  "  Cyanamid  "  is  not  directly  available 


GUANO  569 

for  plant  food,  but  when  the  "  Cyanamid  "  is  mixed  with 
the  soil,  changes  take  place  by  which  the  combined  nitro- 
gen is  converted  into  substances,  chiefly  ammonium  com- 
pounds, which  can  be  assimilated  by  plants. 

When  calcium  cyanamid  is  treated  with  hot  water,  am- 
monia gas  is  produced : 

CN  .  NCa    +  3  H2O  — >-  2  NH3    +  CaCO3 

calcium  water  ammonia  calcium 

cyanamid  carbonate 

The  ammonia  may  be  passed  into  sulphuric  acid  to  form 
ammonium  sulphate,  a  valuable  fertilizer  (§  508) : 

2NH3    +  H2S04— ^(NH4)2S04 

ammonia          sulphuric  ammonium 

acid  sulphate 

510.  Fish  Scrap.  —  Many  thousands  of  tons  of  menhaden 
or  porgy  are  caught  each  year  on  account  of  the  oil  they 
contain.      After  the  oil  has  been  extracted,  the   scrap  is 
either   dried,   or   partially  dried,   treated  with  sulphuric 
acid,  and  sold  to  manufacturers  of  fertilizers  ;  the  former 
by  the  name  of  "  dry  fish  scrap  "  and  the  latter  under  the 
name    of  "  wet  acid  scrap."     "Dry  fish  scrap"  contains 
about  9  %  of  available  nitrogen.     The  "  wet  acid  scrap  " 
contains  considerably  less. 

511.  Guano  consists  of  the  excrement  of  birds,  together 
with  the  remains  of  the  birds  themselves  and  portions  of 
the  fish  on  which  they  feed.     Extensive  deposits  of  guano 
exist  on  the  islands  along  the  coast  of  Peru.     Peruvian 
guano  was  introduced  into  England  as  early  as  1806,  and 
was  used  in  this  country  not  later  than  1832.     It  has  been 
estimated  that  18,500,000  tons  of  guano  were  used  in  40 
years.     Deposits  30  feet  thick  are  said  to  still  remain  un- 


5TO 


.AGRICULTURE 


touched.     A  good  grade  of  Peruvian  guano  contains  about 
14  %  of  combined  nitrogen. 


FIG.  181.  —  STAPLE  CROPS  :  BEANS. 

512.  Minor  Sources  .of  Nitrogen. — Dried  blood,  cotton- 
seed meal,  hoofs,  horn,  leather,  and  hair  are  of  minor  im- 
portance as  sources  of  nitrogen  for  plant  food.     Leather 
and  hair  are  subjected  to  the  fumes  of  hydrofluoric  acid 
in  order  to  render  available  the  nitrogen  they  contain. 

513.  Fixation  of  Nitrogen.  —  One  method  for  the  conver- 
sion of  the  free  nitrogen  of  the  air  into  compounds  for  use 
as  plant  food  has  already  been  mentioned  in  describing 
the  manufacture  of  "  Cyanamid."     The  problem  of  burn- 
ing the  nitrogen  of  the  air,  thus  causing  it  to  combine 
directly  with  the  oxygen,  has  received  the  attention  of 
several  brilliant  chemists.     The  actual  carrying  out  of  the 


NITROGEN-FIXING   BACTERIA  571 

process  is  one  of  great  difficulty,  because  the  kindling  point 
of  nitrogen  is  above  the  temperature  produced  by  the 
burning,  and  the  temperature  at  which  oxygen  and  nitro- 
gen combine  is  very  near  the  temperature  at  which  the 
resulting  compounds  break  down  into  their  elements. 

Several  companies  have  been  formed  to  produce  nitric 
acid  and  nitrates  by  the  use  of  electrical  energy  to  cause 
the  oxygen  and  nitrogen  of  the  air  to  combine,  thus  form- 
ing oxides  which  can  be  absorbed  by  water  or  by  bases  to 
yield  the  desired  compounds.  The  following  equations 
may  give  the  student  some  idea  of  the  changes  that  take 
place:  +  2  O 


2  — 

nitrogen         oxygen  nitrogen 

peroxide 

2  NO2  +  H2O  -^-  HNO2  +  HNO 

nitrogen        water  nitrous  nitric 

peroxide  acid  acid 


2HNO2+    O2    —  ^ 

nitrous  oxygen  nitric 

acid  acid 

2  HNO3  +  Ca(OH)2  —  ^2  H2O  +  Ca(NO3)2 

nitric  calcium  water  calcium 

acid  hydroxide  nitrate 

Some  of  the  companies  are  at  present  meeting  with  suc- 
cess and  bid  fair  to  become  important  factors  in  the  pro- 
duction of  fixed  nitrogen. 

514.  Nitrogen-fixing  Bacteria.  —  While  flowering  plants 
do  not  possess  the  power  to  absorb  directly  from  the  air 
the  nitrogen  needed  to  build  up  their  tissues,  some  of  them 
are  able  to  derive  their  nitrogen  from  parasitic  plants 
which  grow  on  their  roots.  These  nitrogen-fixing  bacteria 
are  able  to  take  nitrogen  directly  from  the  air  which  is 
mixed  with  the  soil  in  which  they  grow.  Leguminous 
plants,  such  as  clover,  beans,  and  peas,  frequently  obtain 
much  t)f  their  nitrogen  from  the  nitrogen-fixing  bacteria 


572 


AGRICULTURE 


growing  on  their  roots.  The  infected  roots  have  wartlike 
growths  or  nodules  on  them,  caused  by  colonies  of  bacteria 
(Fig.  182).  The  earth  around  the  nodule-bearing  roots 

contains  millions  of  germs 
ready  to  attack  the  roots  of 
similar  plants  not  infected. 
Such  soil  can  be  used  to 
inoculate  a  soil  lacking  in 
the  desired  germs.  The 
bacteria  draw  nourishment 
from  the  plants  on  whose 
roots  they  grow,  but  do 
much  more  good  than  harm. 
When  a  plant,  for  example 
clover,  which  has  obtained 
its  nitrogen  from  the  air  by 
the  assistance  of  nitrogen- 
fixing  bacteria,  is  plowed 
under,  the  soil  is  enriched 
in  organic  matter  containing 
nitrogen  which  is  rapidly 
rendered  available.  Cul- 
tures '  of  nitrogen-fixing 
bacteria,  for  example, 
"  Farmogerm "  and  "  Ferguson's  Composite  Culture  of 
Nitrogen-fixing  Bacteria,"  are  at  present  on  the  market 
and  can  be  used  to  inoculate  the  seed  of  leguminous 
plants. 

Nitrogen-fixing  bacteria  will  not  thrive  in  an  acid  soil. 
It  is,  therefore,  useless  to  inoculate  a  sour  soil  with  them. 
The  acids  in  the  soil  must  be  neutralized  by  the  applica- 
tion of  some  alkali  ;  in  other  words,  the  soil  must  be 
"sweetened."  Finely  ground  limestone  is  probably  the 
best  substance  to  use  for  this  purpose.  * 


Copyright  by  The  Scientific  American. 


FIG.  182.  —  BEAN  ROOTS  SHOWING 
NODULES. 


NITROGEN  FERTILIZERS  573 

515.  Nitrification.  —  The  breaking  down  of  organic  com- 
pounds containing  unavailable  nitrogen  into  compounds 
containing  available  nitrogen  is  called  nitrification.     Such 
chemical  changes  are  brought  about  by  low  forms  of  life, 
the  nitrifying  bacteria. 

Substances  such  as  stable  manure,  dried-  blood,  dried 
fish  scrap,  and  cotton-seed  meal  contain  nitrogen  com- 
pounds readily  attacked  by  the  nitrifying  bacteria,  which 
are  always  present  in  air  and  in  soils.  Three  sets  of  bac- 
teria take  part  in  the  process  of  nitrification  :  one  set  con- 
verts the  organic  nitrogen  into  ammonia,  a  second  set 
changes  the  ammonia  into  nitrites,  and  the  third  set  con- 
verts the  nitrites  into  nitrates.  The  ammonia  formed  may 
escape  into  the  air  and  much  valuable  fertilizing  material 
may  thus  be  lost.  When  the  odor  of  ammonia  is  noticed 
around  a  stable  or  a  manure  pile,  the  farmer  should  real- 
ize that  a  valuable  nitrogen  compound  is  passing  beyond 
his  control,  and  he  should  apply  some  absorptive  material 
such  as  earth  or  ground  gypsum.  Ammonia  produced  in 
the  soil  is  not  lost,  because  it  is  rapidly  changed,  by  the 
action  of  the  nitrifying  bacteria,  into  nitrous  acid  and 
nitrites. 

516.  The  Choice  of  Nitrogen  Fertilizers.  —  The    soluble 
nitrogen  compounds,  such  as  sodium  nitrate  and  ammo- 
nium  sulphate,  contain  nitrogen   in   a  directly  available 
form.     They  are  readily  soluble  and  are  rapidly  leached 
from   the  soil.     These  compounds  should,  therefore,   be 
applied  shortly  before  they  are  needed  by  the  crop.     They 
are    of    especial    value    for    use   in    intensive    farming. 
"  Cyanamid,"  which  will   undoubtedly  become  a  valued 
source  of  fixed  nitrogen,  is  not  readily  soluble  in  water,  and 
therefore  is  less  likely  to  be  leached  from  the  soil  than 
nitrates. 


574  AGRICULTURE 

Where  legumes  are  to  be  raised  for  the  market,  or  where 
it  is  profitable  to  produce  a  crop  of  them  to  be  plowed 
under,  the  nitrogen-fixing  bacteria  furnish  a  valuable 
means  of  supplying  nitrogen  to  the  soil.  Guano,  dried 


FIG.  183.  —  A  FIELD  OF  CLOVER. 

fish  scrap,  cottonseed  meal,  and  dried  blood  are  too  limited 
in  quantity  and  distribution,  and  are  usually  too  expensive, 
for  general  use  as  fertilizers.  Leather  scrap,  dried  gar- 
bage, and  peat  are  used  to  improve  the  mechanical  con- 
dition of  a  fertilizer  for  use  in  seed  drills  rather  than  on 
account  of  the  plant  food  they  contain. 

SOURCES   OF  PHOSPHORUS 

The  rock  phosphates,  phosphatic  slag  from  iron  and 
steel  furnaces,  bone,  the  Peruvian  and  Caribbean  guanos, 
and  mineral  phosphate  are  important  sources  of  phos- 
phorus. 

517.  Rock  Phosphates  is  a  term  applied  to  deposits  directly 
traceable  to  an  organic  origin  ;  they  contain  calcium  phos- 
phate which  has  been  derived  from  the  bones  of  animals. 


SOURCES   OF  PHOSPHORUS  575 

t 

Large  deposits  of  rock  phosphates  occur  in  the  United 
States.  The  deposits  found  in  Florida,  Tennessee,  and 
South  Carolina  have  been  extensively  worked,  while 
those  of  Utah,  Idaho,  and  Wyoming  have  not  yet  been 
developed. 

518.  Phosphatic  Slag.  —  When  an  iron  ore  contains  com- 
bined phosphorus,  it  is  necessary  to  separate  the  phos- 
phorus from  the  iron  during  the  process  of  smelting  and 
refining,   as  phosphorus  renders  iron  and  steel  weak  at 
ordinary  temperatures.     This  separation  is  accomplished 
by  lining  the  furnace   with  the  oxides  of   calcium  and 
magnesium  and  adding   these   substances  to  the  furnace 
charge.     The  slag  produced  is  of  great  value  as  a  source 
of  phosphorus  for  crops.     It   is   now  believed   that  the 
phosphorus  exists  in  the  slag  as  a  double  salt,  calcium 
phosphate  and  calcium  silicate,  and  as  iron  phosphate. 

519.  Bone.  —  The  mineral  ingredients  of   bone    consist 
almost  entirely  of   calcium  phosphate  and  calcium  car- 
bonate.    Bones  have  long  been  used  as  a  source  of  phos- 
phorus for  farm  crops. 

520.  Guano.  —  Peruvian  guanos  contain  about  4.4  %  of 
combined    phosphorus     (10  %     P2O5).      The    Caribbean 
guanos  contain,  on  the  average,  more  than  double  that 
amount,  although  they  are  very  poor  in  nitrogen. 

521.  Apatite  is  a  mineral  consisting  of  calcium  phosphate 
in  combination  with  calcium  chloride  and  calcium  fluoride. 
It  furnishes  the  only  common  illustration  of  a  mineral 
phosphate,  that  is,  a  substance  containing  phosphorus  whose 
origin  cannot  be  traced  directly  to  an  organic  source. 
Large  quantities  of  apatite  were  formerly  imported  from 
Canada  for  use  in  the  manufacture  of  commercial  fertilizers. 


576 


AGRICULTURE 


The  expense  of  mining  apatite  does  not  permit  it  to  enter 
into  general  competition  with  the  rock  phosphates. 


FIG.  184.  —  STAPLE  CROPS:    HAY. 


522.  The  Calcium  Phosphates.  —  Calcium  has  a  valence  of 
2  and  phosphoric  acid  (H3PO4)  is  tribasic.  The  formula 
for  normal  calcium  phosphate  is,  therefore,  Ca3(PO4)2. 
This  is  variously  known  as  tricalcium  phosphate,  rock 
phosphate,  and  bone  phosphate.  Two  calcium  acid  phos- 
phates are  known:  dicalcium  phosphate,  Ca2H2(PO4)2, 
and  monocalcium  phosphate  or  "  superphosphate  of  lime," 
CaH2(P04)2. 

Dicalcium  phosphate  goes  in  trade  by  the  name  of  "  re- 
verted phosphoric  acid."  It  may  be  formed  by  a  re- 
action between  monocalcium  phosphate  and  tricalcium 
phosphate  : 


CaH4(P04)2 

monocalcium 
phosphate 


Ca8(P04)2 

tricalcium 
phosphate 


2Ca2H2(PO4)2 

dicalcium 
phosphate 


or  by  a  reaction  between  calcium  phosphate  and  sulphuric. 
acid: 


THE    CALCIUM  PHOSPHATES  577 

Ca3(P04)2    +    H2S04  -^  CaS04  +   Ca2H2(PO4)2 

tricalcium  sulphuric  calcium  dicalcium 

phosphate  acid  sulphate  phosphate 

The  molecule  of  dicalcium  phosphate,  Ca2H2(PO4)2. 4  H2O, 
contains  4  molecules  of  water  of  crystallization. 

Dicalcium  phosphate  is  not  soluble  in  water,  but  is 
readily  soluble  in  neutral  ammonium  citrate,  and  is  soluble 
in  juices  secreted  by  plant  roots.  It  makes  up  the  so- 
called  "  citrate  soluble  phosphoric  acid "  of  commercial 
fertilizers. 

Monocalcium  phosphate,  when  it  occurs  in  fertilizers,  is 
termed  "  soluble  phosphoric  acid "  because  it  is  readily 
soluble  in  water  and  directly  absorbed  by  plants.  It  is 
prepared  by  the  action  of  sulphuric  acid  on  tricalcium 
phosphate.  The  final  equation  representing  the  reaction 
is  commonly  written: 

Ca3(P04)2  +  2  H2S04— ^2  CaS04  +  CaH4(PO4)2 

tricaloium  sulphuric  calcium  monocalcium 

phosphate  acid  sulphate  phosphate 

This  equation  does  not  take  into  account  the  water 
of  crystallization  of  either  the  monocalcium  phosphate 
(CaH4(PO4)2 .  H2O)  or  that  of  the  crystallized  calcium 
sulphate  (CaSO4  .  2  H2O). 

Monocalcium  phosphate  together  with  the  dicalcium 
phosphate  constitutes  the  available  phosphoric  acid  of 
commercial  fertilizers. 

Tricalcium  phosphate  is  insoluble  in  water  and  in 
neutral  ammonium  citrate.  It  constitutes  the  unavail- 
able phosphoric  acid  of  a  fertilizer.  In  the  soil  it  slowly 
becomes  available,  and  gradually  yields  a  supply  of  phos- 
phorus to  plants  for  several  years.  The  sum  of  the  mono-, 
di-,  and  tri-calcium  phosphates  is  the  total  phosphoric  acid 
of  a  fertilizer. 


578 


AGRICULTURE 


523.  Sources  of  Potassium.  —  Potassium  enters  the  virgin 
soil  chiefly  through  the  disintegration  of  clay-producing 
rocks,  such  as  granite  and  syenite,  both  of  which  contain 
potassium  feldspar. 

Potassium  chloride,  derived  from  extensive  deposits  in 
Germany,  is,  at  the  present  time,  the  principal  potassium 
compound  used  as  a  fertilizer. 

Potassium  sulphate  is  also  used  in  fertilizers,  but  is  not 
so  cheap  a  source  of  potassium  as  the  chloride. 

Kainite,  MgSO4  .  KC1 .  3  H2O,  a  compound  also  imported 
from  Germany,  is  another  source  of  potassium  for  agricul- 
tural purposes.  The  formula  for  kainite  shows  that,  in 
addition  to  potassium,  it  contains  the  elements  magnesium 
and  sulphur,  which  are  essential  to  plant  life. 

Wood  ashes  contain  soluble  potassium  compounds  and 
would  be  of  great  value  as  a  source  of  potassium  for  plant 

food  if  the  supply  were 
large. 

Potassium  feldspar, 
which  occurs  in  this 
country  in  enormous 
quantities,  contains 
from  12%  to  17%  of 
potash.  Thus  far  no 
method  economically 
profitable  has  been 
found  for  converting  it 
into  compounds  con- 
taining potassium  in  a 
soluble  form.  While 
rocks  containing  potassium  silicates  are  being  weathered 
slowly,  and  the  potassium  which  they  contain  is  being 
made  available,  the  process  does  not  go  on  with  sufficient 
rapidity  to  meet  the  demands  of  farm  crops.  On  the 


FIG.  1 85.  —  STAPLE  CROPS  :  POTATOES. 


TERM   USED  IN  MARKET   QUOTATIONS        579 

other  hand,  the  fact  that  the  potassium  is  largely  con- 
tained in  insoluble  silicates  assures  a  large  supply  of  re- 
serve plant  food.  Economic  necessity  will  eventually 
require  the  chemist  to  discover  methods  of  making  the 
potassium  of  feldspars  available.  At  present,  the  solu- 
tion of  the  problem  does  not  seem  to  be  far  distant. 

524.  Term  Used  in  Market  Quotations.  —  The  nitrogen  con- 
tent of  a  fertilizer  may  be  guaranteed  as  "  available  nitro- 
gen," as  "ammonia,"  or  as  "units  of  ammonia."  By 
"  available  nitrogen  "  is  meant  nitrogen  contained  in  com- 
pounds which  may  be  assimilated  by  plants.  The  "  per- 
centage of  ammonia "  does  not  mean  that  the  fertilizer 
actually  contains  ammonia,  but  that  it  contains  available 
nitrogen  in  a  quantity  equal  to  that  in  the  per  cent  of 
ammonia  named.  By  the  term  "unit  of  ammonia"  is 
meant  a  quantity  of  available  nitrogen  equal  to  that  con- 
tained in  1  %  of  ammonia.  A  few  examples  may  make  the 
meaning  of  these  terms  clear.  A  fertilizer  is  guaranteed 
to  contain  2  %  of  ammonia.  What  is  the  least  amount  of 
available  nitrogen  it  should  contain  ? 

Taking  the  atomic  weight  of  nitrogen  as  14.  Oi1  and  that 
of  hydrogen  as  1.008,  the  molecular  weight  of  ammonia 
may  be  readily  calculated  to  be  17.034. 

N    =  14.010 

H3=    3.024 


17.034 

Of  these  17.034  parts,  14.01  are  nitrogen.  14.01  -f- 
17.034  =  .8225,  or  a  little  over  .8  of  the  2  %  of  ammonia 
would  be  available  nitrogen,  or,  more  exactly,  .8225  X  2  % 

1  The  exact  atomic  weights  (International  Committee  standard)  are 
used  in  the  calculations  for  fertilizers.  A  small  variation  in  the  atomic 
weight  might  mean  a  difference  in  pounds  when  a  calculation  involves  a 
ton  of  fertilizer. 


580  AGRICULTURE 

or  1.645  %.  In  other  words,  each  100  pounds  of  the  fer- 
tilizer should  contain  1.645  pounds  of  available  nitrogen  ; 
and  a  ton,  or  2000  pounds,  would  contain  20  x  1.645  pounds 
or  32.9  pounds. 

Now  the  nitrogen  might  be  contained  in  the  fertilizer 
in  various  compounds,  for  example,  sodium  nitrate,  dried 
fish  scrap,  or  tankage.  How  much  sodium  nitrate  guar- 
anteed to  contain  95  %  of  NaNO3  would  be  required  to 
yield  32.9  pounds  of  nitrogen?  This  quantity  can  be 
found  by  the  following  calculation  : 

Na  =  23.00 

N   =  14.01- 

O3  =  48.00 

85.01 

If  85.01  pounds  of  pure  sodium  nitrate  would  yield  14.01 
pounds  of  nitrogen,  85.01-^14.01  or  6.07  pounds  of  so- 
dium nitrate  would  yield  1  pound  of  nitrogen;  32.9  x 
6.07,  or  199.7  pounds  of  pure  sodium  nitrate  would  be  re- 
quired for  one  ton  of  the  fertilizer  guaranteed  to  contain 
2  %  of  ammonia.  But  the  commercial  sodium  nitrate  was 
only  95  %  pure.  Therefore  199.7  pounds  is  only  95  %  of 
the  quantity  of  commercial  sodium  nitrate  required.  The 
actual  amount  required  would  be  199. 7  -r- . 95  or  210.2 
pounds.  Thus  we  have  calculated  that  210.2  pounds  of 
95  %  sodium  nitrate  would  be  required  in  each  ton  of  a 
fertilizer  to  have  it  contain  2  %  of  nitrogen  reckoned  as 
ammonia,  or  1.64  %  of  available  nitrogen. 

If,  instead  of  using  sodium  nitrate  to  furnish  the  ni- 
trogen for  the  2  %  ammonia  fertilizers,  a  tankage  con- 
taining 6  units,  or  6  %,  of  ammonia  were  employed,  the 
amount  of  tankage  required  per  ton  of  fertilizer  can  be 
calculated  as  follows : 

Two  per  cent  of  ammonia  is  40  pounds  per  ton.     One  ton 


TERM   USED  IN  MARKET   QUOTATIONS         581 

of  the  6  %  tankage  in  question  would  contain  120  pounds 
of  nitrogen  reckoned  as  ammonia ;  y4^  or  ^  of  a  ton  of  the 
tankage  would  be  required  per  ton  of  the  fertilizer.  If 
the  value  of  the  fertilizer  is  indicated  in  terms  of  nitrogen, 
this  value  may  be  converted  into  terms  of  ammonia  by  multi- 
plying the  percentage  of  nitrogen  by  1.2151  or  17. 034 -f- 
14.01. 

The  combined  phosphorus  in  a  fertilizer  is  generally 
guaranteed  in  terms  of  phosphoric  acid,  by  which  is  meant 
not  the  compound  H3PO4  but  its  anhydride  P2O5.  The 
terms  "  soluble,"  "  available,"  and  "  total  phosphoric  acid  " 
are  often  used  in  connection  with  the  guarantee.  The 
meaning  of  these  has  already  been  explained.  The  mono-, 
di-,  and  tri-calcium  phosphate  content  is  always  reduced 
to  terms  of  phosphoric  anhydride.  This  may  be  readily 
accomplished  by  considering  monocalcium  phosphate 
to  be  CaO  .  2  H2O  .  P2O6,  dicalcium  phosphate  to  be 
2  CaO .  H2O  .  P2O5,  tricalcium  phosphate  to  be  3  CaO  .  P2O5, 
and  then  making  use  of  a  method  similar  to  that  employed 
in  the  reduction  of  ammonia  to  terms  of  nitrogen.  The 
phosphoric  acid  (P2O5)  content  of  a  fertilizer  can  also  be 
readily  converted  into  terms  of  rock  phosphate  (Ca3PO4). 

The  combined  potassium  contained  in  a  fertilizer  is 
usually  reckoned  in  terms  of  "  potash  ";  that  is,  the  chemi- 
cal compound  having  the  formula  K2O.  Potassium  chlo- 
ride may  be  considered  as  having  been  formed  by  a  reaction 
between  potash  (K2O)  and  hydrochloric  acid  (HC1): 

K20   +       2HC1     — •>•  H20   +     2KC1 

potash  hydrochloric  water  potassium 

acid  chloride 

By  use  of  this  equation,  the  relation  between  the  potash 
content  of  a  fertilizer  and  potassium  chloride  may  be 
readily  calculated. 

Numbers  are  often  used  to  indicate  the  plant  food  con- 


582  AGRICULTURE 

tained  in  a  fertilizer ;  for  example,  it  is  spoken  of  as  a  4-8-2 
or  a  9-20  fertilizer.  The  first  of  these  numbers  relates  to 
the  percentage  of  nitrogen,  the  second  to  the  percentage 
of  "  phosphoric  acid  "  (P2O5),  and  the  third  to  the  per- 
centage of  "  potash "  (K2O)  contained  in  the  fertilizer. 
A  4-8-2  fertilizer  contains  4  %  of  nitrogen,  8  %  of  "  phos- 
phoric acid,"  and  2  %  of  "potash."  A  9-20  fertilizing 
material  contains  9  %  of  nitrogen  and  20  %  of  "  phos- 
phoric acid."  As  may  be  seen  from  the  above  figures,  a 
fertilizer  always  contains  a  large  per  cent  of  inert  material. 

525.  Soil  Stimulants.  —  Combined    calcium    is   generally 
added  to  the  soil  in  the  form  of  air-slaked  lime,  made  by 
exposing  quicklime,  CaO,  to  the  atmosphere.     Air-slaked 
lime  consists  of  calcium  hydroxide  mixed  with  calcium 
carbonate.     It  is  of  value,  not  on  account  of  the  plant  food 
it  contains,  but  on  account  of  its  power  to  neutralize  acids 
.in  the  soil,  and  its  power  to  convert  unavailable  substances 
into  plant  food.     It  should  never  be  forgotten  that  the 
soil  is  not  being  made  permanently  richer  by  the  addition 
of  lime,  but,  on  the  contrary,  its  application  aids  in  the 
more  rapid  exhaustion  of  the  soil      This  has  been  recog- 
nized by  the  agriculturalists  of  Europe,  and  has  given  rise 
to  such  proverbs  as  "  Lime  makes  a  rich  father  and  a  poor 
son." 

Slaked  lime  is  caustic  in  its  action,  that  is,  it  destroys 
organic  matter.  It,  therefore,  decreases  the  amount  of 
organic  matter  in  the  soil.  This  is  in  most  cases  undesir- 
able. The  greater  length  of  time  lime  remains  exposed 
to  the  air,  the  greater  the  quantity  of  calcium  carbonate 
it  contains  and  the  less  caustic  it  becomes. 

526.  Limestone.  —  The  addition  of  very  finely   ground 
limestone  to  the  soil  has  in  many  cases  proved  valuable 
on  account  of  its  ability  to  neutralize  undesirable  acids  in 


FARM  PROBLEMS 


583 


the  soil.  It  often  contains  magnesium  compounds  and 
fossils  which  may  yield  calcium  phosphate.  Limestone  is 
not  caustic  in  its  action  and  increases  rather  than  dimin- 
ishes the  fertility  of  the  land  to  which  it  is  added.  It  is, 
therefore,  preferable  to  lime. 

527.  Gypsum.  —  Ground  gypsum,  or  "  lanct  plaster,"  aids 
in  the  liberation  of  plant  food  from  insoluble  compounds 
in  the  soil.     It  acts  less  rapidly  than  lime,  and  is  not  so 
valuable  for  neutralizing  acids.     On  the  other  hand,  it  has 
comparatively  little  influence  on  the  organic  matter  of  the 
soil,  and,  in  this  respect,  is  superior  to  lime. 

528.  Farm  Problems  and  Scientific  Knowledge.  —  The  time 
when  the  uneducated  and  untrained  man  can  be  a  suc- 
cessful farmer  is  rapidly __ 

passing.     A  knowledge 

of  the  composition  and 
nature  of  the  soil  to  be 
tilled,  and  of  the  crops 
to  be  raised,  is  essential. 
The  farmer  should  know 
whether  his  land  needs 
a  complete  fertilizer, 
that  is,  one  containing 
nitrogen,  phosphoric 
acid,  and  potash,  or  a 
fertilizer  containing 
only  one  or  two  of  these 
substances.  He  should 
have  information  con- 
cerning the  sources  and  prices  of  fertilizing  materials  and 
be  able  to  calculate  the  substance  which  will  furnish  the 
most  of  the  desired  element  or  elements  for  the  least 
money.  He  should  understand  that  the  amount  of  an 


FIG.  1 86.  —  STAPLE  CROPS  :    WHEAT. 


584 


AGRICULTURE 


element  taken  from  the  soil  varies  with  the  crop  and 
should  be  able  to  plan  a  desirable  rotation  of  crops.  He 
should  know  when  to  use  a  large  supply  of  available 
plant  food,  and  when  it  will  pay  to  use  a  fertilizer  con- 
taining material  that  will  slowly  be  converted  into  plant 
food.  He  should  understand  the  value  of  fertilizing  ma- 
terials produced  on  the  farm,  and  should  know  how  to  pre- 
vent the  waste  of  any  of  them. 

But  these  are  only  a  few  of  the  problems  the  farmer  has 
to  face.  Equally  important  are  the  mechanical  condition 
of  the  soil,  the  quality  of  the  seed  planted,  and  the  kind 
of  stock  raised.  He  must  understand  the  utility  of  farm 
implements,  know  the  pests,  both  insect  and  parasitic, 
which  attack  his  crops,  and  how  to  reduce  their  depreda- 
tions to  a  minimum.  In  fact,  each  farmer  has  his  own 
problems  to  solve  ;  problems  whose  solution  requires  as 
much  scientific  knowledge  and  business  skill  as  any  other 
industry  demands. 

CONSTITUENTS   OF   STAPLE   CROPS 

In  the  following  table,  the  nitrogen,  the  phosphorus, 
and  the  potassium  content  of  some  staple  crops  is  given  in 
terms  corresponding  to  the  numbers  used  to  indicate  the 
plant  food  contained  in  a  commercial  fertilizer  (§  524,  pp. 

581-582). 


10 

)  POUNDS  OF  CHOP 

CONTAIN 

ILLUSTRATION 

Nitrogen 

Phosphorus  (P2O5) 

Potassium  (K2O) 

IK  TEXT 

Corn  (seed)     .     . 

1.8011). 

0.572  Ib. 

0.373  Ib. 

Fig.  178 

Oats  (seed)      .     . 

1.76  Ib. 

0.687  Ib. 

0.482  Ib. 

Fig.  180 

Wheat  (seed)  .     . 

2.08  Ib. 

0.758  Ib. 

0.518  Ib. 

Fig.  186 

Potatoes  (tubers) 

0.84  Ib. 

0160  Ib. 

0.578  Ib. 

Fig.  185 

Beans  (seed)    .     . 

3.90  Ib. 

0  962  Ib. 

1.217  Ib. 

Fig.  181 

Clover  Hay  (in  bud) 

2.45  Ib. 

0.710  Ib. 

2.591  Ib. 

Fig.  183 

Hay  (air  dry)  .     .     . 

1.05  Ib. 

0.343  Ib. 

0.964  Ib. 

Fig.  184 

SUMMARY  585 

SUMMARY 

Elements  Essential  to  Plant  Life  are  calcium,  carbon,  hydrogen, 
iron,  magnesium,  nitrogen,  oxygen,  phosphorus,  potassium,  and 
sulphur.  A  soil  is  likely  to  become  deficient  in  compounds  of 
nitrogen,  phosphorus,  and  potassium,  and  consequently  become 
infertile. 

A  Complete  Fertilizer  contains  compounds  of  nitrogen,  phos- 
phorus, and  potassium  in  forms  suitable  for  plant  food. 

Sources  of  Nitrogen  valuable  for  use  in  fertilizers  are  sodium 
nitrate,  ammonium  sulphate,  calcium  cyanamid,  and  various 
organic  substances  such  as  guano,  dried  blood,  and  cottonseed 
meal. 

Fixation  of  Nitrogen  is  the  conversion  of  the  free  nitrogen  of  the 
air  into  useful  compounds.  This  is  brought  about  by  chemical 
processes,  and  by  the  action  of  cultures  of  nitrogen-fixing  bacteria. 

Nitrification  is  the  conversion,  by  processes  of  decay,  of  ni- 
trogenous organic  compounds  into  compounds  that  can  be  absorbed 
by  the  roots  of  plants.  It  is  accomplished  by  bacteria. 

The  Chief  Sources  of  Combined  Phosphorus  for  use  in  fertilizers 
are  the  rock  phosphates,  mineral  phosphates,  bones,  Peruvian 
guano,  and  phosphatic  slag  from  iron  blast  furnaces. 

Monocalcium  Phosphate  is  soluble  and  directly  available  as  plant 
food. 

Dicalcium  Phosphate,  "reverted  calcium  phosphate,"  is  not 
soluble  in  water,  but  can  be  dissolved  by  the  root  juices  of  plants, 
and  for  this  reason  is  available. 

Tricalcium  Phosphate  is  not  available  for  plant  food  until  it  has 
been  converted  into  some  soluble  compound. 

Sources  of  Combined  Potassium  for  use  in  fertilizers  are  potas- 
sium chloride,  potassium  sulphate,  kainite,  and  wood  ashes. 


586  AGRICULTURE 

• 
EXERCISES 

1.  Why  should  the  farmer  be  familiar  with  the  "  Law  of 
Conservation  of   Matter "  which  states    that  matter  is   inde- 
structib.le,  and  that  something  cannot  be  made  from  nothing  ? 

2.  Of  the  ten  elements  necessary  to  plant  life,  name  three 
that  are  most  likely  to  be  lacking  in  a  soil. 

3.  What  is  meant  by  the  fixation  of  nitrogen  ? 

4.  Briefly  describe  two  chemical  processes  for  the  fixation 
of  nitrogen. 

5.  What  are  nitrogen-fixing  bacteria,  and  under  what  condi- 
tions do  they  flourish  ? 

6.  Under  what  circumstances  is  it  advantageous  to  make 
use  of  nitrogen-fixing  bacteria  ? 

7.  Define  nitrification  and  describe  the  steps  in  the  process. 

8.  What  is  meant  by  the  terms  soluble,  reverted,  insoluble, 
and  available  when  used  in  connection  with  the  phosphoric  acid 
of  a  fertilizer  ? 

9.  Mention  important  compounds  of  potassium  used  in  fer- 
tilizers. 

10.  What  is  a  complete  fertilizer  ? 

11.  What  is  a  4-8-2  fertilizer  ? 

12.  A  commercial  lot  of  sodium  nitrate  is  guaranteed  to  be 
91  %  pure.     What  is  the  least  quantity  of  available  nitrogen 
that  should  be  contained  in  one  ton  of  the  substance  ? 

13.  A  sample  of  muriate  of  potash  was  reported  by  a  com- 
petent analyst  to  contain  48  %  of  potash.     What  per  cent  of 
potassium  chloride  did  the  sample  contain  ? 

14.  A  fertilizer  is  guaranteed  to  contain  2.43  %  of  ammonia. 
This  is  equivalent  to  what  per  cent  of  nitrogen  ? 

15.  A  sample  of  soluble  bone  phosphate  was  found  to  contain 
14  %  of  soluble  phosphoric  acid.     How  many  pounds  of  mono- 
calcium  phosphate  per  ton  would  it  contain  ? 


EXERCISES  587 

16.  A  sample  of  tankage  is  guaranteed  to  contain  6  units  of 
ammonia.     What  is  the  percentage  content  of  nitrogen  ? 

17.  When  nitrogen  is  worth  19  cents  a  pound,  and  phos- 
phoric acid  31  cents  a  pound,  what  is  the  commercial  value  of 
a  9-20  (9  %  ammonia-20  %  bone  phosphate)  tankage  ? 

18.  Making  use  of  the  quotations  given  below^  calculate 

(a)  the  quantities  of  nitrate  of  soda,  dissolved  S.  C.  rock, 

and  muriate  of  potash  ; 
(6)  the  cost  of  each  ; 
(c)  the  number  of  pounds  of  inert  matter  required  for 

one  ton  of  a  3-9-7  fertilizer. 

Market  quotations : 

Nitrate  of  soda,  15  %  nitrogen ....  $  57.00  per  ton 
Dissolved  S.  C.  rock,  14  %  available  P205  .  12.60  per  ton 
Muriate  of  potash,  48  %  K20 48.00  per  ton 

19.  Sometimes  experiment  stations  publish  factors  by  the 
use  of  which  the  approximate  "commercial  valuation"  of  a 
fertilizer  can  be  calculated.     The  "commercial  valuation"  is 
the  retail  cash  price  in  dollars  per  ton  of  the  unmixed  constit- 
uents of  the  fertilizer.     Such  a  table  reads : 

Multiply  the  percentage  of  nitrogen  by 3.8 

Multiply  the  percentage  of  available  phosphoric  acid  by  .     0.9 
Multiply  the  percentage  of  insoluble  phosphoric  acid  by  .     0.4 
Multiply  the  percentage  of  potash  by    .......  1.00 

The  factors  of  course  vary  with  the  price. 

Making  use  of  the  factors  given  above  calculate  the  commer- 
cial valuation  of  a  fertilizer  guaranteed  to  contain  — 

Nitrogen .    V^. ;;; .'  . ".     .       1.31% 

Available  phosphoric  acid  .  ;- '  V '  ."  -J;--a:'  ..  .  .  9.87 
Total  phosphoric  acid  .  .  .  •  i"  ;  Y  H'  .  .  .  11.34 
Potash  .  .  .  .  ,  .  ,;:  v  .  -  ,  '  .  ^V  ^  .  .  5.41 

The  insoluble  phosphoric  acid  equals  the  total  phosphoric 
acid  minus  the  available  phosphoric  acid. 


CHAPTER    XLVI 

CHEMICAL  CALCULATIONS 

529.  Molecular  Weight.  —  The  molecular  weight  of  an 
element,  or  of  a  compound,  may  be  readily  calculated  from 
its  formula.     For  example,  the  formula  for  ordinary  oxygen 
is  O2  and  the  atomic  weight  of  oxygen  is  16.     The  molec- 
ular weight  of  oxygen  is,  therefore,  2  x  16  or  32.      The 
molecular  weight  is  always  the  sum  of  the   atomic   weights 
represented  by  the  chemical  formula.     The  formula  for  sul- 
phuric acid  is  H2SO4.     Referring  to  the  table  of  approxi- 
mate atomic  weights  (page  600),  the  student  will  see  that 
the  atomic  weight  of  hydrogen  is  given  as  1,  that  of  sul- 
phur as  32,  and  that  of  oxygen  as  16.     The   molecular 
weight  of  sulphuric  acid  is,  therefore,  98. 

H2  =  2  x  1    =   2 
S  =32 

O4  =  4  x  16  =  64 

98  Molecular  weight  of  sulphuric  acid. 

530.  Specific  Gravity  of  a  Gas  is  the  weight  of  that  gas 
compared  with  the  weight  of  an  equal  volume  of  air  meas- 
ured under  like  conditions.     A  definite  relation  exists  be- 
tween the  specific  gravity  of  a   gas   and    its    molecular 
weight ;  the  molecular  weight  of  a  gas  is  28.9  times  its 
specific  gravity,  or  conversely,  the  specific  gravity  of  gas 
is   3%   of   its  molecular  weight.       If  we  want  to  know 
whether  a  certain  gas  is  heavier  or  lighter  than  air,  we 
simply  have  to  calculate  its  molecular  weight   and  note 
whether  it  is  more  or  less  than  28.9.     If  it  is  more  than 

588 


PROBLEMS  INVOLVING   GASES  589 

28.9,  the  gas  is  heavier  than  air  ;  if  less,  the  gas  is  lighter 
than  air. 

531 .  Vapor  Density  is  the  weight  of  a  given  volume  of  a  gas 
compared  with  the  weight  of  an  equal  volume  of  hydrogen. 
In  other  words,  it  is  the  specific  gravity  of.a  gas  when 
hydrogen  is  taken  as  the  standard  of  comparison.     The 
vapor  density  of  a  gas  is  one  half  of  its  molecular  weight. 
The  molecular  weight  of  a  gas  is  twice  its  vapor  density. 

532.  Weight  of  a  Liter  of  a  Gas.  —  To  calculate  the  weight 
of  a  liter  of  a  gas,  we  may  take  the  weight  of  a  liter  of 
hydrogen  and  multiply  it  by  the  vapor  density  of  the  gas. 
For  example,  to  calculate  the  weight  of  a  liter  of  carbon 
dioxide  measured  at  standard  conditions  (0°  C.  and  at  a 
pressure  equal  to  a  column  of  mercury  760  mm.  high)  we 
proceed  as  shown  below  : 

CO2  is  the  formula  for  carbon  dioxide. 
C  =  12 
02  =  32 

44  Molecular  weight  of  carbon  dioxide. 
44  -r-  2     =22  Vapor  density  of  carbon  dioxide. 
0.09  gram  is  the  weight  of  a  liter  of  hydrogen. 
22  x  .09  g.  =  1.98  g.  Weight  of  a  liter  of  carbon  dioxide. 

533.  Calculations  from  Chemical  Equations  may  be  conven- 
iently divided  into  three  classes,  those  involving  weight 
only,  those  involving  both  weight  and  volume,  and  those 
involving  volume  only. 

534.  Problems  involving  Weight  Only  have  to  do  with  cases 
where  from  a  given  weight  of  one  substance  in  a  reaction 
the  weight  of  some  other  substance  in  the  reaction  is  to 
be  calculated.     For  example,  a  person  desires  to  calculate 
the  number  of  pounds  of  hydrochloric  acid  gas  that  could 
be  obtained  from   500  pounds  of  pure  sodium  chloride. 


590  CHEMICAL   CALCULATIONS 

He  first  writes  the  equation  which  represents  the  reaction 
which  would  take  place  : 

2  NaCl  +  H2S04  — >-  Na2SO4  +  2  HC1 

sodium        sulphuric  sodium        hydrochloric 

chloride  acid  sulphate  acid 

He  may  then  state  the  problem  by  placing  500  pounds 
above  the  HC1  and  a  question  mark  above  the  NaCl: 

?  Ib.  500  Ib. 

2  NaCl  +  H2SO4  — >-  Na2SO4  +  2  HC1 

Now  the  same  relation  exists  between  actual  weights  as 
exists  between  the  weights  represented  by  the  chemical 
equation.  2  HC1  represents  2  x  36.5  or  73  parts  by 
weight,  and  2  NaCl  represents  2  x  58.5  or  117  parts  by 
weight.  Therefore,  117  :  73  ::  x  Ib.  :  500  Ib. 

x=  801+  pounds  of  sodium  chloride. 

The  solution  of  the  problem  may  be  briefly  stated  as 
follows  : 

?lb.  500  Ib. 

2  NaCl  +  H2S04  -^-  Na2SO4  +  2  HC1 

117  73 

Na  =  23  H  =    1 

Cl  =  35.5  Cl  =  35.5 

58.5x2  =  117  36.5  x  2  =  73 

117  :  73  ::xlb.  :  500  Ib. 
x  =  801  +  Ib.  of  sodium  chloride. 

535.  Problems  involving  Both  Weight  and  Volume  include 
cases  in  which  the  object  is  to  determine  the  weight  of  a 
certain  compound  required  for  the  production  of  a  given 
volume  of  a  gas,  or  vice  versa.  The  solution  of  this  class 
of  problems  with  the  least  amount  of  work  possible  re- 
quires a  knowledge  of  the  generalization  that  when  weights 
are  expressed  in  grams,  every  molecule  of  gas  represented 


WEIGHT  AND   VOLUME  591 

by  the  equation  stands  for  22.2  liters  ;  when  weights  are 
expressed  in  kilograms  every  molecule  of  gas  stands  for 
22.2  cubic  meters  ;  and  when  weights  are  expressed  in 
ounces  (avoirdupois)  each  molecule  of  gas  stands  for 
22.2  cubic  feet. 

Suppose  the  problem  to  be  :  What  weight  of  calcium 
carbide  would  be  required  for  the  production  of  1000 
cubic  feet  of  acetylene  ?  The  chemical  equation  repre- 
senting the  reaction  is 


CaC2  +  2  H20—  ^Ca(OH)2  +     C2H2 

calcium  water  calcium  acetylene 

carbide  hydroxide 

Since  the  atomic  weight  of  calcium  is  40  and  that  of  car- 
bon 12,  CaC2  stands  for  64  parts  by  weight.  As  the 
problem  calls  for  cubic  feet  of  acetylene,  we  would  con- 
sider these  parts  by  weight  to  be  ounces.  Now,  remem- 
bering that  when  parts  by  weight  are  taken  as  ounces, 
each  molecule  weight  of  the  gas  stands  for  22.2  cubic 
feet,  we  see  that  64  ounces  of  calcium  carbide  would  yield 
22.2  cubic  feet  of  acetylene.  The  calculation  of  the  num- 
ber of  ounces  of  calcium  carbide  required  to  yield  1000 
cubic  feet  of  acetylene  then  becomes  a  simple  matter. 
The  problem  and  its  solution  may  be  represented  as 
follows  : 

x  oz.  1000  cu.  ft. 

CaC2  +  2  H2O  —  >-  Ca(OH)2  +  C2H2 
64  oz.  22.2  cu.  ft. 

Ca  =40  C2H2  =  1  molecule  of  acet- 

C2  =  2xl2  =  24  ylene   and   in   the  problem 

64  stands  for  22.2  cu.  ft. 

64  :  22.2  :  :  x  :  1000 
x  =  288.  2  +  oz.  or  18.0+  Ib.  ' 

If  two  molecules  of  the  gas  mentioned  in  the  problem 
are  represented  in  the  equation,  the  volume  of  the  gas  is 


592  CHEMICAL   CALCULATIONS 

22.2  x  2  or  44.4  cubic  feet,  cubic  meters,  or  liters,  accord- 
ing to  whether  the  parts  by  weight  represent  ounces, 
kilograms,  or  grams.  For  example,  suppose  the  problem 
to  be  :  How  many  liters  of  ammonia  can  be  obtained  by 
heating  20  grams  of  ammonium  sulphate  with  sufficient 
slaked  lime  ?  The  equation  for  the  reaction  and  the  so- 
lution of  the  problem  may  be  represented  as  follows  : 

20  g.  x  liters 

(NH4)2SO4  +  Ca(OH)2—  *-  CaSO4+  2  H2O  +  2  NH3 
132  g.  2x22.2 

or  44.4  liters 
of  ammonia. 
N   =14 
H4  =  J 

18x2=    36 
S  =32 


132     . 

132  :  44.4  :  :  20  :  x 
x  —  6.7+  liters. 

536.  Problems  involving  volume  only  are  simple  to  solve, 
because  the  same  relation  exists  between  the  volumes  of 
gases  that  exists  between  the  numbers  of  molecules  of  the 
same  gases  represented  in  the  chemical  equation.  Suppose 
that  we  wish  to  calculate  the  number  of  liters  of  oxygen 
required  for  the  complete  combustion  of  250  liters  of 
acetylene.  The  equation  which  represents  the  reaction  is  : 

2  C2H2  +     5  02—  ^4  CO2  +  2  H2O 

acetylene  oxygen  carbon  water 

dioxide 

This  shows  that  2  molecules  of  acetylene  require  for 
complete  combustion  5  molecules  of  oxygen,  and  conse- 
quently 2  volumes  of  acetylene  require  5  volumes  of 


PREPARATION  OF  A    SOLUTION  593 

oxygen.  The  problem  and  its  solution  may  therefore  be 
stated  as  follows : 

'2501.     xl. 

2  C2H2  +  5  O2  — >-4  CO2  +  2  H2O 

21.  51. 

21.  :51.  ::2501.  :  xl. 

x  =  625  1.  of  oxygen. 

537.  Preparation  of  a  Solution  of  Desired  Specific  Gravity. — 

It  frequently  becomes  necessary  to  prepare  a  solution  of 
some  desired  specific  gravity  from  one  of  the  more  concen- 
trated solutions  purchased  from  dealers  in  chemicals.  For 
instance,  one  may  wish  to  prepare  a  solution  of  sulphuric 
acid  having  a  specific  gravity  of  1.20  by  the  addition  of 
water  to  the  commercial  acid  having  a  specific  gravity  of 
1.84.  How  many  cubic  centimeters  of  acid  and  how 
many  of  water  would  be  required  to  make  1000  cubic 
centimeters  of  the  solution  having  a  specific  gravity  of  1.2? 

A  formula  for  the  solution  of  such  problems  may  be 
derived  as  follows : 

Let   x  =  number  of  cubic  centimeters  of  heavier  liquid. 

Let   y—  number  of  cubic  centimeters  of  lighter  liquid. 

Let  M—  specific  gravity  of  the  desired  mixture. 

Let  H  —  specific  gravity  of  the  heavier  liquid. 

Let  L  =  specific  gravity  of  the  lighter  liquid. 

Let  V  —  volume  of  the  mixture. 

We  would  then  have 

(1)  x  +y  =  Fand 

(2)  Hx  +  Ly=  VM. 
Multiplying  (1)  by  L  we  obtain 

(3)  Lx  +  Ly  =  LV. 
Subtracting  (3)  from  (2)  we  get 

(4)  ffx-Lx=  VM-  LVor  x(H-  L)  =  V(M- L). 


594  CHEMICAL    CALCULATIONS 

Therefore 

(5)  *-r. 


Having  derived  the  formula  just  given,  the  solution  of  the 
problem  given  above  becomes  merely  a  matter  of  substi- 
tuting for  H,  L,  M,  and  V  the  values  assigned  to  them 
and  then  solving  for  x.  In  the  problem 

#=1.84 
L  =1.00 
M=  1.20  and 
V=  1000  cubic  centimeters. 

Making  the  proper  substitutions  in  the  formula  we 
obtain 

x  =  !'!?""  !'nn  x  1000  or      |5  x  1000  or  238.1  c.c. 
1.84  —  1.00  84 

Therefore,  238.1  cubic  centimeters  of  sulphuric  acid  hav- 
ing a  specific  gravity  of  1.84  should  be  added  to  761.9 
cubic  centimeters  of  water  in  order  to  obtain  1000  cubic 
centimeters  of  a  dilute  acid  having  a  specific  gravity  of  1.2. 
The  formula  given  does  not  take  into  account  any 
change  in  volume  which  may  occur  on  mixing  the  liquids 
used,  but  it  is  sufficiently  accurate  for  use  in  most  of  the 
cases  that  will  arise  during  laboratory  work  in  an  ele- 
mentary course  in  chemistry. 

538.  Normal  Solutions.  —  A  normal  solution  is  a  solution 
a  liter  of  which  contains  either  1  gram  of  replaceable  hydro- 
gen, or  a  weight  of  an  element,  or  of  a  radical,  that  is 
equal  in  combining  power  to  1  gram  of  hydrogen. 

A  normal  solution  of  an  add  contains  1  gram  of  replace- 
able hydrogen  per  liter.  To  calculate  the  number  of 
grams  of  acid  per  liter  contained  in  a  normal  solution  of 
an  acid,  divide  the  molecular  weight  of  the  acid  by  the 


PROBLEMS  INVOLVING  NORMAL   SOLUTIONS    595 

number  of  replaceable  hydrogen  atoms  which  the  molecule 
contains. 

A  normal  solution  of  a  base  contains  17  grams  of  hydroxyl 
(OK)  per  liter.  To  calculate  the  number  of  grains  of  a 
base  contained  in  1  liter  of  its  normal  solution,  divide 
the  molecular  weight  of  the  base  by  the  -number  of  OH 
groups  it  contains. 

539.  Problems  involving  Normal  Solutions.  —  When  neu- 
tralization takes  place,  each  acid  hydrogen  atom  has  united 
with  a  hydroxyl  radical  and  vice  versa,  or,  in  other  words, 
a  given  weight  of  hydrogen  (H  =  l)  has  entered  into 
chemical  combination  with  17  times  (OH  =  17)  its  weight 
of  hydroxyl.  It  therefore  follows  that  a  given  volume  of 
a  normal  solution  of  any  acid  will  neutralize  an  equal 
volume  of  a  normal  solution  of  any  base. 

The  fact  just  mentioned  is  of  great  service  in  making 
calculations  connected  with  titration  work ;  that  is,  with 
the  determination  of  the  unknown  concentration  of  a  solu- 
tion by  making  use  of  a  solution  of  known  concentration. 
Suppose  that  a  chemist  finds  that  15  cubic  centimeters  of  a 
fifth-normal  (N/5)  solution  of  hydrochloric  acid  exactly 
neutralizes  30  cubic  centimeters  of  a  solution  of  sodium 
hydroxide  of  unknown  concentration,  and  he  desires  to 
calculate  the  number  of  grams  of  sodium  hydroxide  per 
liter  that  its  solution  contains.  If  the  solution  of  sodium 
hydroxide  had  been  fifth-normal,  30  cubic  centimeters  of 
fifth-normal  hydrochloric  acid  would  have  been  required 
to  neutralize  30  cubic  centimeters  of  the  base.  But  it 
only  required  15  cubic  centimeters  of  the  fifth-normal  acid 
to  neutralize  30  cubic  centimeters  of  the  base.  The  solu- 
tion of  the  base  was  therefore  ^  of  fifth-normal  or  half 
as  concentrated  as  the  acid.  Now  a  normal  solution  of 
sodium  hydroxide  contains  40  grams  of  sodium  hydroxide 


596  CHEMICAL   CALCULATIONS 

Na=23 


per  liter 


OH  =  17 


A  fifth-normal  solution  of  sodium 


40 

hydroxide  would  contain  ^°-  or  8  grams  of  sodium  hydroxide 
per  liter,  and  the  solution  in  question  would  contain  ^-|  of 
8  grams  or  4  grams  of  sodium  hydroxide  per  liter. 


SUMMARY 

Specific  Gravity  is  the  weight  of  a  substance  compared  with 
the  weight  of  an  equal  volume  of  a  substance  taken  as  a  stand- 
ard. The  weight  of  the  standard  is  considered  to  be  1.  Water 
is  the  standard  for  liquids  and  solids.  Air  is  usually  considered 
as  the  standard  for  gases. 

Vapor  Density  is  a  term  used  in  place  of  specific  gravity  when 
hydrogen  is  the  standard.  The  vapor  density  of  a  gas  is  the 
number  of  times  that  gas  is  as  heavy  as  an  equal  volume  of 
hydrogen,  measured  under  like  conditions.  The  vapor  density  of 
a.  gas  is  equal  to  one  half  its  molecular  weight. 

The  Weight  of  a  Liter  of  a  Gas  equals  the  weight  of  a  liter  of 
hydrogen  multiplied  by  the  vapor  density  of  the  gas  (0.09  g.  x 
v.d.). 

In  Solving  Problems  Involving  Weight  Only,  the  student  should 
remember  that  actual  Weights  are  proportional  to  the  weights 
represented  by  the  chemical  equation  involved. 

For  the  Solution  of  Problems  Involving  Weight  and  Volume,  it  is 

convenient  to  make  use  of  the  generalization  that,  when  weights 
are  expressed  in  grams,  each  molecule  of  gas  represented  in  the 
chemical  equation  stands  for  22.2  liters. 

During  the  Solution  of  Problems  Involving  Volume  Only,  the 

student  should  bear  in  mind  the  fact  that  the  same  relation  exists 
between  volumes  that  exists  between  the  numbers  of  molecules 
of  gases  represented  by  the  equation. 


EXERCISES  597 

A  Normal  Solution  of  an  Acid  contains  1  gram  of  replaceable  hy- 
drogen per  liter. 

A  Normal  Solution  of  a  Base  contains  1 7  grams  of  hydroxyl  per 
liter. 

EXERCISES 

Making  use  of  the  data  given  and  the  table  of  atomic 
weights  on  page  600,  solve  the  following  problems : 

1.  Calculate    the     molecular     weights     of      03   ,      N2     , 

ozone    nitrogen 

CO2        ,          HC1  ,  and  NajBA. 

carbon  dioxide    hydrogen  chloride  borax 

2.  What  is  the  specific  gravity  of    NH3   ,       C12  ,        H2   , 

ammonia    chlorine    hydrogen 

N2      ,       C02        ? 

nitrogen    carbon  dioxide 

3.  What   is   the   vapor   density   of       02     ,          CO          , 

oxygen    carbon  monoxide 

S02       ,    C2H2  ,       N20      ? 

sulphur  dioxide  acetylene  nitrous  oxide 

4.  Calculate   the  weight  of  one  liter  of  oxygen,  nitrogen, 
carbon  dioxide,  ammonia,  acetylene. 

5.  How   many  pounds  of  combined   nitrogen  are  there  in 
one  ton  of  sodium  nitrate,  NaNO3? 

6.  A  cubic  foot  of  water  weighs  62.5  pounds.     A  cubic  foot 
of  cast  iron  weighs  462.5  pounds.    What  is  the  specific  gravity 
of  cast  iron  ? 

7.  The  specific  gravity  of  lead  is  11.3.  Calculate  the  weight 
of  1  cubic  foot  of  lead. 

8.  The   specific  gravity  of   concentrated  sulphuric  acid  is 
1.84.     How  many  cubic  feet  are  there  in  1  ton  of  sulphuric 
acid? 

9.  Oak  is  0.8  as  heavy  as  water.    What  does  a  cubic  foot  of 
oak  weigh? 

10.  Cork  is  0.3  as  heavy  as  oak ;  what  is  its  specific  gravity  ? 


598  CHEMICAL   CALCULATIONS 

11.  How  many  pounds  of  hydrogen  and  how  many  pounds 
of  oxygen  can  be  obtained  by  the  decomposition  of  50  pounds 
of  water  ? 

12.  Salt  and  sulphuric  acid  react  to  form  hydrogen  chloride 
and  sodium  sulphate.     How  much  salt  would  be  consumed  in 
the  preparation  of  20  pounds  of  sodium  sulphate  ? 

13.  What  is  the  percentage  composition  of  ammonium  sul- 
phate (NH4)2S04  ? 

14.  When  nitric  acid  is  added  to  calcium  carbonate,  carbon 
dioxide,  water,  and  calcium  nitrate  are  formed  according  to 
the  equation : 

CaC03       +  2  HN03  — >•  Ca(NO3)2  +   H20  +     C02 

calcium  carbonate      nitric  acid  calcium  nitrate      water    carbon  dioxide 

How  many  cubic  feet  of  carbon  dioxide  would  be  liberated  from 
5  pounds  of  calcium  carbonate  by  the  action  of  sufficient  nitric 
acid? 

15.  When   water   is   added   to    calcium    carbide,    calcium 
hydroxide  and  acetylene  result : 

CaC2      +    2  H20  — >-     Ca(OH)2     +        C2H2 

calcium  carbide         water  calcium  hydroxide         acetylene 

What  weight  of  calcium  carbide  would  be  required  for  the 
production  of  2500  cubic  feet  of  acetylene?  What  weight 
would  be  required  if  the  calcium  carbide  were  only  87  %  pure? 

16.  What   volume   of   oxygen  would   be   required  for  the 
complete  combustion   of   1000  cubic  feet  of  acetylene?     Air 
contains  21  %  of  oxygen.     What  volume  of  air  would  be  re- 
quired ? 

17.  What  volume  of  carbon  dioxide  would  be  obtained  by 
the  complete  combustion  of  1000  cubic  feet  of  marsh  gas? 

CH4       +  2  02      — >-       C02  +      2  H2O 

marsh  gas          oxygen  carbon  dioxide  steam 

18.  How  much  iron  could  be  obtained  from  200  tons  of  an 
ore  containing  90  %  of  ferric  oxide,  Fe203? 

19.  What   volume   of   hydrochloric  acid  having  a  specific 
gravity  of  1.2,  and  what  volume  of  water,  would  be  required 


EXERCISES  599 

to  make  1  liter  of  hydrochloric  acid  having  a  specific  gravity 
of  1.1? 

20.  A  merchant  wants  to  prepare  5  liters  of  ammonia  water 
with   a   specific  gravity  of   0.96  by  diluting  ammonia  water 
having  a  specific  gravity  of  0.9.     What  volume  of  the  concen- 
trated ammonia  water  and  what  volume  of  w^ter  should  he 
use  ? 

21.  Calculate  the  number  of  grams  of  each  of  the  following 
compounds  contained  in  its  normal  solution:     HN03,  H2S04, 
H(C2H302),  KOH,  Ca(OH)2,  Na2S04. 

t22.  21  cubic  centimeters  of  a  normal  solution  of  nitric  acid 
were  required  to  neutralize  15  cubic  centimeters  of  a  solution 
of  potassium  hydroxide.  How  many  grams  of  KOH  per  liter 
did  the  solution  of  potassium  hydroxide  contain  ? 

23.  15.2   cubic   centimeters  of  fifth-normal  sulphuric   acid 
were  required  to  neutralize  18.7  cubic  centimeters  of  a  solution 
of  ammonium  hydroxide.     What  was  the  concentration  of  the 
ammonium  hydroxide  solution  ? 

24.  16.3  cubic  centimeters  of  half-normal  sodium  hydroxide 
solution  were  required  to  neutralize  10.5  cubic  centimeters  of 
a  solution  of  sulphuric  acid.     Calculate  the  concentration  of 
the  sulphuric  acid. 


PHYSICAL  CONSTANTS 
OF  THE  IMPORTANT-  ELEMENTS 


ELEMENT. 

SYMBOL. 

ATOMIC  WEIGHTS. 

VALENCE. 

SPECIFIC  GRAVITY. 

MELTING 
POINT. 

BOILING 
POINT. 

Approx- 
imate. 

Exact 
0=16. 

Water  =  1. 

Air  =  l. 

°C. 

°C. 

Aluminum 

Al 

27 

27.1 

Ill 

2.7 

657 

2200 

Antimony 

Sb 

120 

120.2 

III  V 

6.6 

630 

1600 

Argon 

A 

40 

39.88 



1.38 

-188 

-186 

Arsenic 

As 

75 

74.96 

Ill  V 

5.7 

.  .  . 

<360 

volatile 

Barium 

Ba 

137 

137.37 

II 

3.8 

'  850 

960 

Bismuth 

Bi 

208 

208.0 

III  V 

9.7 

269 

1436 

Boron 

B 

11 

11.0 

III 

2.4 

infusible 

3500 

Bromine 

Br 

80 

79.92 

I 

3.1 

-7.3 

59 

Cadmium 

Cd 

112 

112.4 

II 

8.6 

322 

778 

about 

Calcium 

Ca 

40 

40.09 

II 

1.8 

780 

.  .  . 

amorphous 

Carbon 

C 

12 

12.00 

IV 

1.4-1.9 

infusible 

3500 

Chlorine 

Cl 

35.5 

35.46 

I 

2.49 

-102 

-33.6 

Chromium 

Cr 

52 

52.0 

II  III  VI 

6.9 

1520' 

Cobalt 

Co 

59 

58.97 

II 

8.7 

1750 

.  .   . 

Copper 

Cu 

63.6 

63.57 

II 

8.9 

1065 

2100 

Fluorine 

F 

19 

19.0 

1.26 

-223 

-187 

Gold 

Au 

197 

197.2 

III 

19.3 

1062 

2500 

Helium  . 

He 

4 

3.99 



0.13 

-270 

-267 

Hydrogen* 

H 

1 

1.008 

0.07 

-256.5 

-252 

Iodine 

I 

127 

126.92 

4.9 

113 

184 

Iron 

Fe 

56 

55.85 

II  III 

7.8 

1550 

.   .  . 

Lead 

Pb 

207 

207.1 

II  IV 

11.3 

327 

1580 

600 


PHYSICAL    CONSTANTS 


601 


ELEMENT. 

SYMBOL. 

ATOMIC  WEIGHTS. 

VALENCE. 

SPECIFIC  GRAVITY. 

MKLTING 
POINT. 

BOILING 
POINT. 

Approx- 
imate. 

Exact 
0=16. 

Water  =  1. 

Air  =  l. 

°C. 

°C. 

Lithium 

Li 

7 

6.94 

I 

0.59 

186 

<1400 

Magnesium 

Mg 

24 

24.32 

II 

1.7 

632 

1100 

Manganese 

Mn 

55 

54.93 

II  IV 

7.4 

1247 

Mercury 

Hg 

200 

200.0 

III 

13.6 

-38.8 

357 

Nickel 

Ni 

58.7 

58.68 

II 

8.7 

1452 

.  .  . 

Nitrogen 

N 

14 

14.01 

III  V 

0.96 

-214 

-195 

Oxygen 

O 

16 

16.00 

II 

1.10 

<-218 

-182 

yellow 

yel 

low 

Phosphorus 

P 

31 

31.04 

III  V 

1.8 

44.1 

290 

Platinum 

Pt 

195 

195.2 

IV 

21.5 

1760 

>  •  . 

Potassium 

K 

39 

39.10 

I 

0.87 

62.5 

667 

Silicon 

Si 

28 

28.4 

IV 

2.4 

1200 

3500 

Silver 

Ag 

108 

107.88 

I 

10.5 

961 

2050 

Sodium 

Na 

23 

23.0 

I 

0.97 

97.6 

877 

Strontium 

Sr 

87 

87.63 

II 

2.5 

900 

white 
heat 

% 

rhombic 

Sulphur 

S 

32 

32.07 

II  IV  VI 

2.0 

114.5 

444.6 

Tin 

Sn 

119 

119.0 

II  IV 

7.0-7.3 

232 

1525 

Zinc 

Zn 

65 

65.37 

II 

7.1 

419 

918 

INDEX 


References  are  to  pages.    Heavy-face  numerals  indicate  the  principal 
reference. 


Abrasives 416,  461 

Accumulator,  chloride    .     .     .    443 

Acetate  of  lime 375 

Acetic  acid     ......  20,  225 

Acetone 375 

Acetylene  ....       Ill,  137,  210 

burners 137 

series 210 

Acid  radical 60 

Acids Chap.  Ill,  14 

characteristics 18 

common      18 ;  Chap.  XLIV,  534-546 

definition 21 

Actinic  power 349 

Adulteration  of  foods    ...    263 

Aeration  of  water 174 

Agriculture         .     Chap.  XLV,  562 
Air,  character  .     .     .  Chap.  XV,  144 

composition 144 

minor  constituents      ....    153 

physical  character 144 

Alcohol,  as  a  fuel 107 

denatured 217 

ethyl 215 

grain 215 

methyl 214 

wood 214 

Alcoholic  beverages      ...    218 

Alcohols 213 

Aldehydes 222 

Alkalies,  definition 31 

Alkyl  radical 214 

Alloys 197 

Alpaca 322 

Alum  baking-  powder    ...    273 

Aluminum 405 

bronze 201 

extraction  of 406 

sulphate 558 

Alundum 463 

Amalgams 199,  410 


Amendments,  soil 567 

Ammonia 549 

in  air 153 

in  illuminating  gas      ....  377 

liquid 550 

preparation,  synthetic     .     .     .  549 

source 549 

uses 550 

water 30 

water  in  cleaning 306 

Ammonium,  chloride  ....  40 

group 30 

hydroxide 30 

sulphate 558 

sulphate  as  fertilizer  ....  567 

Amorphous  substances     .    .  84 

Amyloid 233 

Analin 239 

Anesthetics 211,237 

Anhydrides,  acid,  definition     .  69 

Animal  fibres 322 

Animal  life,  relation  to  air  .    .  145 

Anode 3,431 

Apatite  in  fertilizers  ....  575 

Aquadag- 423 

Aqua  fortis 20 

Aquaregia .539 

Aromatic  series 238 

Ash 104 

Atmosphere 144 

Atomic  weights 50 

table  of 600 

Atoms 47 

Autogenous  welding1     .    .     .  391 

Babbitt  metal 199 

Bacillus  bulgaricus    ....  289 

Bacteria,  in  air    ......  151 

in  milk 280 

nitrifying 573 

nitrogen  fixing 571 


603 


604 


INDEX 


References  are  to  pages. 


Baking,  of  bread 269 

of  meats 261 

Baking  powders 272 

alum 273 

cream  of  tartar 272 

healthfullness  of 273 

phosphate 272 

Baking  soda 558 

Barometer 144 

Bases Chap.  IV,  23 

action  on  organic  matter      .     .      26 

action  with  acids 27 

characteristics 29 

definition 59 

nomenclature 63 

preparation 23 

uses 29 

Basic  lining,  in  furnaces  ...    473 

Bauxite 405 

Beer 218 

Bell  metal 200 

Benzene 238 

Benzine 372 

Benzoic  acid 239 

Benzol 238 

Bessemer  converter  ....    472 

Beverages,  alcoholic    ....    218 

Binary  compounds     ...     55, 63 
Blast  furnace      .     .     .     .     .     .468 

Blast  lamps  .      Chap.  XXXIII,  385 

Blaugas 139 

Bleaching,  of  cotton     .    .    .     .332 

of  linen 332 

of  silk .333 

of  wool 333 

Bleaching  agents  in  launder- 
ing   310 

Bleaching  powder      ....    555 
Blowpipe,  oxyacetylene   .\   .     .    389 

oxyhydrogen .   5,  387 

Blowpipes  .    .    Chap.  XXXIII,  385 

Blowtorch 386 

Blueprints 344 

Bluing 308 

Boiler  scale 184 

Boilers,  foaming  in 186 

pitting  of 186 

Bone  in  fertilizers 575 

Boneblack '  .    236 

Boracic  acid   .  19 


Borax  .     .     , 

in  cleaning 
Boric  acid  . 
Brandy  .  . 
Brass  . 


558. 
306 
19 
219 
200 


Bread,  baking  of 269 

crust  of  . 270 

kneading  of 269 

porous  structure  of      ....  268 

rising  of 269 

salt-rising 271 

Bread  making    Chap.  XXXIV,  267 

use  of  yeast  in 268 

Brick Chap.  XLII,  506 

fire 509 

glazed 509 

making  of 506 

vitrified 508 

Briquettes 105 

Bristol  brick 462 

Broiling 261 

Bronze     . 200 

aluminum 201 

phosphor 200 

Building  materials     .... 

Chap.  XLI,  490 

Building  stones 500 

Bunsen  burner 122 

Burner,  acetylene 137 

bunsen 122 

fishtail 134 

gas 134 

gasoline 128,  134 

gas  range 124 

kerosene 133 

self-lighting 137 

Burning Chap.  X,  91 

conditions  necessary  for       .     .  94 

definition 96 

energy  change 96 

extinguishing 95 

simple  types 9 

Burnt  sienna 359 

Butane 206 

Butter 295 

adulterated 296 

process 296 

renovated 296 

Butterine 296 

Butyric  acid 225 


INDEX 


605 


References  are  to  pages. 


Cadmium  yellow 359 

Calcium 25 

carbide 111,417 

rotary  furnace 418 

hydroxide,  formation  of  ...      25 

hypochlorite 554 

light 5,  388 

oxide,  manufacture     ....    490 

sulphate 495 

Candles ....    132 

Canned  goods     .     .    .    .     .     .    264 

Caramel  . 237 

Carat 202 

Carbides 417,419 

Carbohydrates  .."....    232 

in  foods 244 

Carbolic  acid 238 

Carbon  compounds    .... 

Chaps.  XIX,  XX,  205 

Carbon  dioxide,  in  air     ...    149 

in  beverages        ......    219 

in  bread  making      .....    268 

in  fermentation       ....    216 

in  fire  extinguishers    ....      95 

Carbon  disulphide      ....    424 

Carbon  monoxide  .     .     .     .93,  117 

Carbon  tetrachloride     .    .    .    212 
Carbonates  as  ores    .     .     .     .403 

Carborundum     ..'....    419 

for  cleaning  metals'     ....    463 

Cashmere    ........    322 

Cassiterite 413 

Cast  iron 468,  485 

Cathode,  definition  ....   3,  431 

Caustic  potash 29,  554 

Caustic  soda 29,  553 

Cave  formation 182 

Cell,  Daniell 439 

dry     . 441 

Exide 443 

gravity 440 

Leclanche  .' 441 

sal-ammoniac      .    .    .     .     .     .    440 

storage 442 

Cells,  polarization  in     ....    439 

primary 438 

Celluloid 233 

Cellulose 232,  323 

Cement   ....      Chap.  XLI,  490 
coating  for  iron 457 


hydraulic    . 496 

manufacture 496 

Portland 496 

setting  of 498 

Centrifugal  niters 162 

Champagne 219 

Charcoal     . 347 

Cheese .297 

American    ........    298 

cottage 297 

Chemical  calculations  .    .    . 

Chap.  XL VI,  588 

Chemical  change 1 

Chemical  glassware  ....    528 

Chemical  problems,  weight    .    589 

weight  and  volume      ....    590 

volume 592 

Chemical  purification    .    .    . 

Chap.  XVI,  157 
Chemicals,  commercial    .     .    . 

Chap.  XLIV,  533 

analyzed 534 

C.P 53f 

crude 534 

purity 533 

technical 534 

Chile  saltpeter   ...  .41 

China 510 

English 514 

Sevres 514 

Chinese  wood  oil 360 

Chloride  accumulator  .     .    *    443 

Chloride  of  lime 555 

Chlorine,  in  bleaching  .  310,  331,  332 
in  water  purification   ....     180 

process  for  gold 411 

Chloroform 211 

Chrome  steel 487 

Chrome  yellow 358 

Citric  acid 18 

Clay 506 

Cleaning,  dry 309 

Cleaning  and  laundering  .     . 

Chap.  XXVI,  302 
Coagulation,     water     purifica- 
tion by 179 

Coal 102 

cannel    .     .     .    .    .    .    .    .     .    105 

distillation  of       Chap.  XXXII,  376 
gas 108,  377 


606 


INDEX 


References  are  to  pages. 


Coatings,  protective,  for  iron   .  456 

Cobalt  blue 358 

Coin  alloys 202 

Coke 376 

Collodion 233 

Colored  glass 527 

Coloring  in  foods 263 

Color  photography    ....  349 

Combination,  direct  .     Chap.  II,  8 

definition 73 

Combustion,  ordinary     ...  91 

products  of 93 

spontaneous 97 

Compound,  binary  .     .     .     .     55,  63 

definition 6 

Concrete 498 

Conduction  of  electricity      .  430 
Conductivity  of  metals     .     .  192 
Contact     process     for    sul- 
phuric acid 540 

Converter,  Bessemer   ....  472 

Cooking  of  foods   Chap.  XXII,  260 
Copper,    in    combination    with 

sulphur 8 

corrosion  of 454 

electrolytic  refining  of     ...  447 

sulphate 38 

Cordials 219 

Corrosion  of  metals   .... 

Chap.  XXXVIII,  452 

prevention  of 454 

Cottdn 323 

mercerized 324 

Cream,  butter,  cheese  .    .    . 

Chap.  XXV,  293 

Cream 293 

whipped 293 

Cream  of  tartar 272 

Crocus,  for  polishing    ....  463 

Crops,  common,  constituents  of  584 

Croton  water,  analysis    ...  169 

Cryolite 406 

Crystallization 82 

definition 165 

purification  by 163 

Cupola  furnace 479 

Cyanamid 567 

Cyanide  process  for  gold  .     .  411 

Daniell  cell                                ,  439 


Decomposition,  direct,  defini- 
tion   73 

of  mercuric  oxide 2 

of  water 3 

Definite  proportions,  law  of  .  46 
Denatured  alcohol  ....  217 
Destructive  distillation  .  .  374 

of  coal 376 

of  wood 374 

Dextrin   . 235 

Dextrose 215 

Diastase 215 

Dicalcium  phosphate  .  .  .  577 
Digestion,  enzymes  in .  .  .  .263 
Disease,  transmission  by  water  171 
Dishes,  manufacture  .  ...  512 

Disinfectants 223, 555 

Dissociation  theory  ....  431 
Distillation,  definition  ...  164 

destructive 374 

of  coal 376 

of  wood 374 

purification  .by 158 

Driers,  paint 363 

Drop  forgings 480 

Dry  cell 441 

cleaning 309 

Ductility  of  metals    ....    194 

Dust  in  air 151 

Dutch  process  for  white  lead    354 

Dyes  and  dyeing 

Chap.  XXIX,  336 

Dyes,  acid 338 

basic a39 

direct  developed 338 

direct  for  cotton 336 

modern 336 

sulphur 339 

vat 340 

Dynamite 231 

gelatin 232 

Edison  storage  cell    ....    443 

Electric  furnaces 

Chap.  XXXVI,  417 
Electricity,  conduction  of  .  .  430 
Electrochemical  series ...  58 

Electrochemistry 

Chap.  XXXVII,  430 
development  of 430 


INDEX 


607 


References  are  to  pages. 


Electrolysis,  explanation  of     .  432 

of  water 3 

Electrolytes 430 

Electrolytic  refining  of  metals 

446 

Electroplating- 445 

copper 445 

gold 448 

nickel 456 

silver 448 

Electro-silicon 463 

Electrotyping     : 446 

Element,  definition 6 

negative 56 

positive 56 

Elements,  physical  constants    .  600 

symbols  of 48 

Elutriation 420 

Emeraude  green 359 

Emery 463 

Emulsion ' 85 

Energy  requirement  in  foods  246 

Engine,  automobile 401 

combustion  in 400 

Engines,  gas    .    Chap.  XXXIV,  396 

gasoline 400 

kerosene 400 

Enzymes  in  digestion    .     .    .  263 

Epsom  salts 40 

Equations,  chemical,  writing  of 

Chap.  VIII,  66 

Esteriflcation 227 

Esters 226 

Etching  of  glass 521 

Ethane 206 

Ether 237 

Ethereal  salts 226 

Ethyl  alcohol 215 

Ethylene 210 

series 209 

Exide  storage  cell 443 

Explosive  mixture     ....  133 
Explosives,  high      ...      231,  234 

Fats 244 

Fatty  acids 225 

Feldspar •   .     .  578 

Fermentation     .....  216 

Fermented  milk 288 

Ferric  oxide  for  polishing      .  463 


Ferrous  sulphate 558 

Fertility  of  soil 562 

Fertilizers 567 

ammonium  sulphate    ....  567 

apatite 575 

bone 575 

calcium  phosphates      ....  576 

cyanamid 567 

fish  scrap 569 

guano 569, 575 

kainite 578 

lime  nitrogen 567 

phosphatic  slag 575 

phosphoric  acid,  available   .     .  577 

citrate  soluble 577 

total 577 

unavailable 577 

potassium  chloride 578 

potassium  sulphate      ....  578 

rock  phosphate 574 

sodium  nitrate 567 

terms  used  in  market  quotations   579 

wood  ashes 578 

Fibres,  animal 322 

plant 322 

Filters,  centrifugal 161 

Fire  brick 509 

Fire  extinguishers     ....  95 
Fireplaces  ....  Chap.  XII,  114 

Fires,  methods  of  putting  out    .  95 

method  of  starting 115 

Fire  test,  kerosene 372 

Fish  oil 360 

Fish  scrap  as  fertilizer  ...  569 

Fixation  of  nitrogen  ....  570 

Flame 102, 132, 134 

bunsen 123 

hottest  part 123 

oxidizing 123 

reducing 123 

Flashing  point 133 

Flour,  wheat 267 

Flux 468 

Foaming  in  boilers     ....  186 

Foods Chap.  XXI,  242 

adulteration 263 

canned 264 

colorings  in 263 

cooking  of  .     .     .     ...     .     .     .  260 

digestion  of ,  262 


608 


INDEX 


References  are  to  pages. 


Foods  —  Continued 

energy  values 246 

mineral  constituents   ....  250 

preservatives  in 263 

protein  requirement    ....  248 

purposes  of 242 

quantity  required 246 

substitution  in 264 

tables 253 

values 244 

Forgings,  drop 480 

Formacone 223 

Formaldehyde 223 

Formalin 223 

Formic  acid 225 

Formulas 49 

chemical,  organic 225 

Fractional  distillation    ...  369 

Freezing,  purification  by      .     .  160 

Fructose 215 

Frying  meats 262 

Fuels Chap.  XI,  101 

characteristics 101 

definition 92,  101 

gaseous 108 

liquid 105 

solid 101 

Furnace,  blast  for  iron     ...  468 

cupola 479 

electric  .    .     .    Chap.  XXXVI,  417 

Heroult 425 

laboratory  .......  417 

rotary  carbide 418 

tin 425 

glass 519 

hot  air 119 

open  hearth 474 

reverberatory 412 

Fusibility  of  metals   ....  195 

Fusible  metals 198 

Gallic  acid 315 

Gallotannic  acid 315 

Galls  for  ink 314 

Galvanized  iron 456 

Gas,  acetylene Ill 

arc 136 

Blaugas 139 

burners 134 

coal ,108 


illuminating 377 

lighters 137 

mantles 136 

natural 110 

oil 139,  371 

Prest-O-Lite 138 

producer 110,  398 

range 123 

stoves     ....     Chap.  XIII,  122 

water 109,  381 

weight  of  a  liter 589 

Gas  engines     .   Chap.  XXXIV,  396 
Gases,  purification  of    ....    157 

solubility 85 

Gasoline 106,  373 

engines 400 

lights 134 

stoves     .     .     .    Chap.  XIII,  122,  128 

Gelatin  dynamite 232 

German  silver 201 

Giant  powder     .     .     .    '.     .     .    232 

Gin 219 

Glacial  acetic  acid      ....      20 

Glass Chap.  XLIII,  516 

aging  of 522 

blowing 523 

Bohemian 516,  518 

chemical  properties     ....    520 

colored 527 

common 516 

cut 525 

etching  of 521 

flint,  composition    .     .     .      517,  518 

furnace 519 

Jena 529 

materials  for 517 

nature 516 

optical    .     . 526 

physical  properties      ....    522 

plate 525 

pressed 524 

window,  composition  .     .     .  516,  518 

manufacture 523 

Glauber's  salt 40 

Glazes,  pottery 511 

Glucose  sugar  (dextrose)    .    .    215 

Gluten    - 267 

Glycerin 229 

Gold,  amalgamation  of      ...    410 
chlorine  process  for     ....    411 


INDEX 


609 


References  are  to  pages. 


Gold  —  Continued 

cyanide  process  for      ....  411 
electrolytic    separation     from 

silver 447 

extraction  of 410 

panning  of 410 

Grain  alcohol 215 

Granite    . 501 

Graphite,  artificial 421 

deflocculated 423 

Gravity  cell 440 

Green  vitriol 558 

Guano 569,  575 

Gun  cotton 233 

Gypsum  in  agriculture      .     .  583 

Hartshorn,  spirits  of    ....  30 

Heroult  electric  furnace   .     .  425 

Hollow  tile 509 

Humidity,  relative 151 

Hydraulic  cement 496 

Hydrocarbons 205 

acetylene  series 210 

aromatic  series 238 

ethylene  series 209 

methane  series 206 

paraffin  series 207 

unsaturated 209 

Hydrochloric  acid      .     .     .  19,  534 

commercial 535 

manufacture 534 

properties  ........  535 

uses  of 536 

Hydrofluoric  acid 521 

Hydrogen,  electrolytic,  manu- 
facture       434 

,      peroxide 556 

preparation     .     . 3 

properties 4 

Hydrogenation  of  oils   ...  228 

Hypo 558 

Hypochlorites 554 

Ice  cream 294 

Illuminating  gas 377 

Illumination 140 

principles  of 140 

values 140 

Indian  red 357 

Infusorial  earth .                      .  461 


Ink Chap.  XXVII,  314 

copying 319 

India 317 

iron 315 

logwood 316 

nigrosin 317 

printers'      . 319 

red     .• 318 

sepia 318 

Invertase 216 

Iodine,  combination  with  mer- 
cury       8 

lodoform 212 

Ion 43J, 

lonization  theory 431 

Iron Chap.  XL,  468 

blast  furnace 469 

cast 468 

casting  of 479 

hardness  of     .......  482 

magnetic  properties     ....  484 

malleability 482 

pig 471 

Kussia 458 

rust 455 

rusting  of 453,  455 

tenacity 482 

uses 485 

wrought 472 

manufacture 478 


Japan  drier 363 

Javelle  water     ....      310, 554 

Kainite  as  fertilizer    ....  578 

Kaolin 506 

Kerosene 107 

fire  test 372 

Kiln,  lime 492 

Kindling-  point 92 

Kitchen  range 118 

Kumiss 288 

Lakes 357 

Lamp,  blast      .    Chap.  XXXIII,  385 

kerosene 132 

Lanolin 328 

Laundering     .     .  Chap.  XXVI,  302 
Lead,  acetate 558 


610 


INDEX 


References  are  to  pages. 


Lead  —  Continued 
burning  .... 
corrosion  of  .  . 
extraction  of  .  . 
pencils  .... 


388 
454 
412 
423 


white 354 

sublimed 355 

Leavening,  by  carbon  dioxide  .  270 

salt-rising 271 

sour  milk 274 

yeast 268 

Leclanche'  cell 441 

Levulose 215 

Light,  calcium 5 

Lights,  oil  and  gas    .  Chap.  XIV,  132 

Lignite 105 

Lime Chap.  XLI,  490 

air  slaked 494 

kiln,  rotary 492 

kiln,  vertical 490 

light 388 

manufacture 490 

slaked 29 

slaking  of 494 

unslaked- 490 

Limestone 502 

in  agriculture 528 

Linen .    .  327 

Linseed  oil 359 

Liqueurs 219 

Litharge 359 

Lithophone 356 

Lubricating  oils     .     .    .     373, 423 

Lye 29 

Magnalium 202 

Magnesium,  combination  with 

oxygen      9 

sulphate 40 

Malleability  of  iron    ....  192 

Malt 215 

Maltose 215 

Manganese,  extraction  of    .     .  408 

steel 486 

Mantles,  gas 135 

Marble 502 

Marsh  gas 207,  208 

Matches 92 

Meats,  baking  of  ......  261 

broiling 261 


frying 262 

roasting 262 

stewing 261 

Melting  points  of  elements  .  602 

Mercerized  cotton     ....  324 

Mercuric  oxide,  decomposition  2 

Mercury,  extraction  of     ...  404 

combination  with  iodine  ...  8 

Metal,  Babbitt 199 

bell 200 

type 201 

Metallic   oxides,   action    with 

acids 37 

Metals,  bearing 199 

chemical  cleaning  of    ....  464 
cleaning  of      .    Chap.  XXXIX,  461 

conductivity 192 

corrosion    .      Chap.  XXXVIII,  452 

ductility 194 

extraction  of  .      Chap.  XXXV,  403 

fusibility 195 

fusible 198 

hardness 196 

malleability 192 

self-protective     .....  454 

typical  properties 

Chap.  XVIII,  192 

Methane 207,  208 

series 206 

Methyl  alcohol 214 

chloride 211 

Milk     .....  Chap.  XXIV,  278 

bacteria  in 280 

certified 283 

composition 278 

condensed 286 

evaporated 285 

fermented 288 

handling  of 279 

homogenized 287 

keeping  sweet 281 

modified 283 

necessity  for  pure 278 

Pasteurized 281 

powdered 287 

preservatives  in 281 

putrefaction  of 280 

sources 279 

souring  of 280 

sterilized 285 


INDEX 


611 


References  are  to  pages. 


Mineral  constituents  of  foods  250 

definition 403 

Mirrors 200 

Miscibility 84 


Mixtures,  explosive      .     . 
Modified  milk     .... 

Mohair 

Molecular  weight .     .     . 
calculation  of  ^~  . 

Molecules 

Mono-calcium  phosphate 
Monochlormethane   .     . 
Mordant . 


133 

283 
322 
50 
588 
•48. 
577 
211 
339 


.Mortar 494 

Multiple  proportions,  law  of  .      47 
Muriatic  acid 19,  535 

Naphtha .371 

Natural  gas 110 

Neutralization,  defined   .     .     28,42 

explanation  of 436 

production  of  salt  by  ....      36 
Nickel,  plating  on  iron      .     .     .    45(5 

steel 486 

Niter 39 

Nitrates 567,  571 

Nitric  acid 20,536 

from  air 539 

in  air 153 

manufacture 536,  539 

properties 537 

uses 538 

Nitrification 573 

Nitrifying  bacteria     ....    573 

Nitrocellulose 233 

Nitrogen 149 

fertilizers 567 

choice  of 573 

fixation  of 570 

in  air 149 

Nitrogen  fixing  bacteria   .     .    571 

Nitroglycerin      : 231 

Nomenclature     .     .    Chap.  VII,  55 
Normal  solutions 594 

Ochre,  yellow 359 

Oil,  drying 97 

flash  point  .     . 133 

gas .     139,  371 

lamp 132 


of  vitriol 20 

petroleum,  heavy 370 

intermediate 371 

light 370 

Oildag 423 

Oils,  hydrogenation  of  .     ...    228 
Oils,  painting    .     ..Chap.  XXXI,  353 

Chinese  wood 360 

fish 360 

linseed 359 

poppy 360 

Oleic  acid 229 

Oleomargarine 296 

Open  hearth  furnace      ...    474 

Optical  glass 526 

Ore,  definition 403 

Ores,  carbonates 403 

sulphides 404 

Organic  acids     ......    224 

Organic  compounds,  nature  of    205 

Oxalic  acid 464 

Oxidation Chap.  X,  91 

slow 96 

Oxides,  carbon  dioxide       10,  91,  116 
carbon  monoxide     .     .     .     .93,117 

magnesium 9 

mercuric 2 

phosphorus 10 

tin 9 

Oxyacetylene  blowpipe    .    .    389 

cutting 393 

Oxy-Blaugas 392 

Oxygen 2,  5 

electrolytic 434 

in  air 144 

nascent       67 

preparation 2,  3 

properties 2,  5 

standard  for  reacting  weights  .      45 
Oxy hydrogen  blowpipe    .     .        5 
Ozone,  in  air    ......     154 

water  purification 180 

Paint  driers 363 

Paints Chap.  XXXI,  353 

enamel 362 

floor 362 

for  iron . 457 

ready  mixed 361 

water 360 


612 


INDEX 


References  are  to  pages. 


Palmitic  acid 225 

Paper,  parchment 233 

waterproof 232 

Paraffin 373 

oil  distillate    .....     371,  373 

series 207 

Paris  green 359 

Pastry 275 

Peat 105 

Pencils,  lead 423 

Pentane 206 

Petroleum 105 

cracking  of 373 

crude 368 

distillation      .      Chap.  XXXII,  368 

purification  of 372 

refining 105,  368 

Phosphates 574 

Phosphor  bronze 200 

Phosphoric    acid    in    fertili- 
zers       577 

available 577 

citrate  soluble 577 

total 577 

unavailable 577 

Phosphorus,     combined     with 

oxygen 10 

forms  of 10 

in  fertilizers 574 

Photographic  plates      .     .     .  346 

prints 348 

toning 348 

Photography  .     .    Chap.  XXX,  344 

color 349 

developer 345 

fixer 345 

sensitive  substance      ....  345 

sensitizer 345 

Physical  constants,  table  of   .  600 

Pig  iron 471 

Pigments    .     .     .  Chap.  XXXI,  353 

blue 358 

colored 357 

definition 353 

green 359 

inert 356 

red 357 

white 354 

yellow 358 

Pitting  of  boilers 186 


Plant  fibres 322 

Plant  life,  relation  to  air       .     .  145 

Plants,  elements  essential  to      .  562 

Plaster 495 

of  Paris 495 

Plate  glass 525 

Plates,  orthochromatic      ...  349 

photographic .346 

Plating,  copper 445 

electrolytic 448 

gold 448 

silver 448 

Plugs,  automatic  sprinkler    .     .198 

fusible 198 

safety 198 

Polarization,  prevention  of  .     .  439 

Polishing  powders     ....  461 

Porcelain 511,  512 

soft 511 

Portland  cement 496 

Potash,  caustic 29 

Potassium    carbonate,    manu- 
facture of 550 

chlorate 555 

chloride 38 

as  fertilizer 578 

cyanide 558 

dichromate 558 

feldspar 578 

ferrocyanide 558 

hydroxide 29 

nitrate 39 

permanganate 558 

sulphate  as  fertilizer  ....  578 
Pottery    ....    Chap.  XLII,  506 

glazes  for 511 

unglazed 509 

varieties 510 

Powder,  baking 272 

giant 232 

polishing 461 

silica 462 

smokeless 234 

Precipitates,    purification    by 

washing 161 

purification  by  filtration      .     .  161 

resulting  from  action  of  ions    .  437 

Precipitation 83 

definition 165 

purification  by 162 


INDEX 


613 


References  are  to  pages. 


Preservatives  in  foods  .     .     .  263 

Prest-O-Lite 138 

Primary  cells 438 

Prints,  photographic     ....  348 

Producer  gas 398 

Propane 206 

Propionic  acid 225 

Protein  requirement  in  foods  248 

Proteins 243 

Protoplasm 243 

Prussian  blue 358 

Puddling-  process 478 

Pumice  for  polishing      ...  462 

Purification,  by  crystallization  163 

by  distillation 158 

by  freezing 160 

of  gases 157 

of  solids 160 

by  sublimation 161 

by  washing 161 

of  water 173 

Purity,  chemical 157 

Putz  pomades 463 

Pyroligneous  acid 375 

Pyroxylin 233 


Quartz     . 
Quicklime 


.  461,  517 
.  25,  494 


Radical,  acid 60 

ammonium 30 

Range,  gas 123 

kitchen 118 

Reacting  weights 45 

Red  lead  in  paints 357 

Refining  of  metals  by  elec- 
trolysis   446 

Replacement,   double,    defini- 
tion  73 

simple,  definition    ....    13,  73 
Reverberatory  furnace      .    .    412 

Roasting  meats 262 

Rock  phosphate 574 

Rouge 463 

Rum 219 

Russia  iron 458 

Rust,  iron 453 

Sal  ammoniac     .....     40, 41 
Salt  33 


Saltpeter 39 

Chile 39 

Salt  rising  bread 271 

Salts Chap.  V,  33 

acid 61 

basic 61 

definition    .     .     ? 21 

effect  on  litmus 40 

ethereal 226 

formation  by  replacement   .    18,  37 

by  neutralization      ....  36 

from  metallic  oxides     ...  37 

important,  tables  of     .     .      41,558 

Sand 494,517 

Sand  filters  for  water    .     .     .  177 

Sandstone 503 

Saponiflcation     ....      228,  230 

definition 239 

Scale,  boiler 184 

Schweitzer's  reagent    ...  232 
Sedimentation,  water  purifica- 
tion   179 

Segger 512 

Seltzer 86 

Series,  electrochemical      ...  58 

Shortening      .......  275 

Sienna,  burnt 359 

Silica,  for  polishing 462 

ware 529 

Silicon  carbide .419 

dioxide 461 

Silk 329 

artificial 325 

Chardonnet 325 

conditioning 331 

ecru 331 

Pauly's 326 

viscose 326 

weighted 331 

Silver,  cleaning  of 464 

bromide  in  photography  .     .     .  346 

corrosion  of 454 

Slag .468 

phosphatic,  fertilizers      .     .     .  575 

Slaked  lime 29 

Smokeless  powder   '.     ...  234 

Soap 302 

adulterations  in 305 

floating 305 

green 305 


614 


INDEX 


References  are  to  pages. 


Soap  —  Continued 

manufacture  of 302 

modified  bases 27 

powdered 306 

scouring 306 

shaving 306 

Soda,  washing 306 

Sodium  bicarbonate  .     .     551,558 

benzoate 239 

carbonate 550 

Solvay  process 550 

chloride 33 

electrolysis  of 432 

hydroxide 23,  552 

Castner  process 552 

hypochlorite 554 

nitrate 39 

as  fertilizer 567 

peroxide 557 

silicate 558 

sulphate 39 

tetraborate 558 

thiosulphate 558 

Softening  of  water     .     .     .     .187 

plants  for 189 

Soil,  amendments 567 

fertility 562 

reserve  material  in      ....    566 

stimulants 582 

Soils,  composition 565 

origin 564 

Solder 198 

Solids,  purification 160 

Solute 77 

Solutions     ....      Chap.  IX,  76 
calculations  for  specific  grav- 
ity     593 

concentrated 79 

definition 77 

dilute 78 

effect  of  temperature  .     .     .   82,  85 

of  pressure 86 

nature 76 

normal 594 

saturated 80 

Solvay  process 550 

Solvent 77 

Specific  gravity  of  a  gas  .  .  588 
Spirits  of  hartshorn  ....  30 
Spontaneous  combustion  97,  99 


Spots,  removal 310 

Stains,  for  wood 362 

oil 363 

removal  of 310 

varnish 363 

water 362 

Starch 234 

Starching    ...'.' 308 

Steam  stills,  petroleum    ...    371 

Stearic  acid    . 225 

Steel Chap.  XL,  468 

alloys 486 

Bessemer 472 

casting  of 479 

chrome 487 

crucible 475 

electric  furnace 476 

electric  refining 425 

half-hard 472 

hard 472 

hardness  of 482 

high  carbon 472,  485 

high  grade 475 

low  carbon 472,  485 

magnetic  properties  of     ...    484 

malleability  of 482 

njanganese 486 

medium  carbon 472,  485 

mild 472 

nature  of 471 

nickel 486 

open  hearth .  474 

soft 472 

tempering 482 

tenacity 482 

tool 472 

tungsten 486 

uses 485 

vanadium 487 

Steels,  uses 485 

alloy 486 

Sterilization  of  water    .     173,  189 

Stewing  meats 261 

Stones,  building 501 

Stoneware 511 

Storage  cells 442 

chloride  accumulator  ....    443 

Edison 443 

Exide 443 

lead 442 


INDEX 


615 


References  are  to  pages. 


..      Chap.  XII,  114 

115 

Chap.  XIII,  122, 123 

Chap.  XIII,  122, 128 

,     118 


Stoves  . 
coal  .  . 
gas  .  . 
gasoline 
kitchen  . 

wood. 117 

Sublimation,  definition    ...  164 

purification  by 161 

Substitution  in  foods     ...  264 

products 210 

Sucrose 236 

Sugar 236 

barley 237 

cane 236 

glucose  (dextrose) 215 

Sugar  of  lead 558 

Sulphides  as  ores 404 

Sulphur 546 

combination  with  copper     .     .  8,  91 

with  oxygen 91 

extraction  of 546 

Louisiana  deposits 547 

uses 549 

Sulphuric  acid   .    .    .    .    .  20,  539 

chamber. process 541 

chemical  properties     ....  544 

contact  process 439 

physical  properties      ....  544 

uses 546 

•Superphosphate  of  lime    .     .  576 

Supporter  of  combustion  .    .  91 

Suspension 78 

Symbols 48 

Synthesis 11 

Tables,  food 253 

elements,  physical  constants  of  600 

Tannic  acid 19,  315 

Tempera  painting 360 

Temperature,  kindling   ...  92 

Tempering  of  steel     ....  482 

Terra  cotta 509 

Textile  materials 

Chap.  XXVIII,  322 

Thermit 408 

welding       ........  408 

Tile,  hollow       509 

Tiles 506 

Tin  chloride    ....  .558 

electric  furnace  .                        .  425 


extraction  of 413 

salt 558 

ware 456 

Toning,  photographic    ....  348 

Torch,  blow 386 

gasoline 134 

Tricalcium  phosphate   ...  577 

Trichlormethane 211 

Tungsten  steel   ......  486 

Turpentine 364,  383 

Type  metal 201 

Ultramarine 359 

Unsaturated  hydrocarbons  .  208 

Unslaked  lime 490 

Valence 55 

defined 62 

important 56 

of  common  elements    ....  62 

satisfaction  of 58 

Vanadium  steel ......  487 

Vapor  density 589 

Varnishes 363 

Vaseline 373 

Vehicle  in  paints 353 

Venetian  red 357 

Ventilation 146 

Vermilion 357 

Vinegar 226 

Viscogen 293 

Vitriol,  blue     .......  41 

oil  of 20 

white 41 

Washing,  clothes 307 

precipitates 161 

soda 306 

Water      ....    Chap.  XVII,  167 

color 169 

commercial  electrolysis   .     .     .  434 

Croton,  analysis  of      ....  169 

decomposition 2 

electrolysis  of 3,  433 

hard 181 

action  with  soap 183 

in  chemical  industries  .    .     .  186 

permanent 183 

temporary 182 

natural  content  .              ...  167 


616 


INDEX 


References  are  to  pages. 


Water  —  Continued 

odor  and  taste 170 

pure  and  wholesome    ....  169 

purification 173 

aeration 174 

chlorination 180 

coagulation 179 

cold 175 

light 175 

mechanical  filters     ....  177 

mechanical  processes    .     .     .  176 

ozonization 181 

sand  filtration 177 

sedimentation 179 

soil  filtration 175 

softeners     ........  188 

softening 187 

softening  plants 189 

sources 167 

sterilization 189 

transmission  of  disease  by  .     .  171  i 

turbidity 78,  87,  170  ; 

value  of 167 

vapor  in  air    .......  150 

Water  gas 380 

enriched 381 

Water  glass 558 

Water-proof  paper     ....  232 
Weight  relations    .      Chap.  VI,  44 

determination  of 44 

Weights,  atomic ......  50 

molecular 50 


reacting 45 

Welding,  autogenous   ....  391 

electric 481 

of  iron 480 

thermit 408 

Whisky 219 

White  lead 354 

sublimed 355 

White  metal 201 

White  vitriol 37 

Whitewash 360 

Whiting 465 

Wines 218 

Wood,  as  fuel 101 

alcohol 214 

ashes,  as  fertilizer 578 

distillation  of      .  Chap.  XXXII,  374 

Wood's  alloy 199 

Wool 328 

Wrought  iron,  manufacture  of  478 

Yeast  .     .     . 216 

in  bread  making      .....  268 

Yellow  ochre 359 

Yellow  prussiate  of  potash  .  558 

Zinc,  corrosion  of 454 

extraction  of 404 

Zinc  chloride 17,  37 

Zinc  oxide,  in  paints    ....    355 

Zinc  sulphate 17,  37 

Zymase    .    .    .    .' 216 


MAR 


1948 

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